“Why did you believe the gospel, but your friend did not? Are you wiser or smarter or more spiritual or better trained or more humble?”
This is typically one of the first questions a Calvinist will ask a non-Calvinist when attempting to convince them of their doctrine. In fact, when I was a Calvinist, I used this argument more often than any other, and it was quite effective. However, I have come to believe there are at least four significant problems with this line of argumentation:
1) Question Begging Fallacy:
As we have discussed HERE, this is a game of question begging because it presumes a deterministic answer is required. It is tantamount to asking, “What determined the response of you and your friend?” As if something or someone other than the responsible agents themselves made the determination. The question presumes determinism is true and that libertarian free will (self-determination) is not possible. 
I believe that the cause of a choice is the chooser (or the cause of a determination is the determiner) and accept the mystery associated with the functioning of that free will in making its own determinations. Now, Calvinists will often challenge my appeal to mystery at this point as if it is a weakness unique to my libertarian worldview. This is a very shortsighted argument, however, which will be made abundantly clear in the next point.
2) Calvinists Ultimately Appeal to the Same Mystery:
While the Calvinist may feel he has the “upper hand” when asking about the “decisive factor” in man’s choice to reject God’s words, the role reverses quite dramatically when the conversation shifts to man’s first choice to reject God’s words. Whether discussing Satan’s first act of rebellion or Adam’s first choice to sin, it becomes quite evident that the Calvinist has painted himself into a corner by denying libertarian free will.
While on the one hand arguing that mankind will always act in accordance with his nature (assuming the nature could not be libertarianly free, mind you), the Calvinist has no rational answer as to why Adam (or Lucifer) chose to rebel.  For instance, John Piper openly admits:
How God freely hardens and yet preserves human accountability we are not explicitly told. It is the same mystery as how the first sin entered the universe. How does a sinful disposition arise in a good heart? The Bible does not tell us.”
And RC Sproul similarly teaches,
“But Adam and Eve were not created fallen. They had no sin nature. They were good creatures with a free will. Yet they chose to sin. Why? I don’t know. Nor have I found anyone yet who does know.”
As you can clearly see, the Calvinist has just “kicked the can down the road,” so to speak, when it comes to appealing to the mystery of free moral will. They eventually appeal to the same mystery that we do, all the while thinking they are taking the higher moral ground by giving God all the credit for the Christian’s choice to repent and trust in Christ. In reality, however, by not accepting the mystery of man’s free will, the Calvinist has created a new mystery that is simply not afforded by the text of scripture.
This problem is made evident by turning the question around and asking this of the Calvinist:
Why has your lost friend continued to hate and reject God?
Most Calvinists do not want to admit that the reprobate of their system ultimately hates and rejects God because God first hated and rejected them. Calvinists would rather focus on the elect who are saved by deterministic means while ignoring the inevitable conclusions about the non-elect who remain damned for the same deterministic reason. In my opinion, this is a dilemma unique to their worldview, not a tension created by the teachings of scripture.
So, the Calvinist rejects the mystery of libertarian freedom only to adopt another even more difficult mystery. One that arguably brings into question the holiness, righteousness and trustworthiness of our God — namely the suggestion that God is implicit in the determination of moral evil, as evidenced by John Calvin’s own teachings:
“…how foolish and frail is the support of divine justice afforded by the suggestion that evils come to be, not by His will but by His permission…It is a quite frivolous refuge to say that God otiosely permits them, when Scripture shows Him not only willing, but the author of them…Who does not tremble at these judgments with which God works in the hearts of even the wicked whatever He will, rewarding them nonetheless according to desert? Again it is quite clear from the evidence of Scripture that God works in the hearts of men to incline their wills just as he will, whether to good for His mercy’s sake, or to evil according to their merits.”
Which mystery is more difficult to swallow? One that seemingly suggests mankind might have some part to play in reconciliation (the bringing together of two parties) or the one that suggests God is the author of evil (that which divided to two parties to begin with)? More importantly, which of these mysteries does the Bible actually afford? (Listen to THIS PODCAST to better understand why a defense of free will is actually a defense of God’s Holiness, not merely an appeal to mystery.)
3) Better by Choice or Divine Decree is Still Better:
Calvinists seem to think there is something morally wrong with admitting that a believer is better than an unbeliever. Of course it is better to believe than it is to “trade the truth of God in for lies.” Whether one believes because they were sovereignly made to do so or simply given the ability to do so freely does not change the fact that believers are doing something “better.” But, as we will discover in the next point, better does not mean worthy of salvation. So, even if the non-Calvinist were to say, “Yes, I’m more humble or smarter,” he would ultimately be saying the exact same thing a Calvinist has to say. The only difference would be that an unbeliever could rightly say to the Calvinist, “How arrogant of you to think that God made you more humble or smarter,” whereas if they said that to the non-Calvinist, we could rightly answer, “No he didn’t, you have no such excuse. You have just as much ability to humble yourself and understand the gospel as I have.”
We (non-Calvinist) are too often accused that we could/would boast in our salvation because we affirm that it is our responsibility to freely respond in faith to the gracious Holy Spirit wrought gospel appeal.
Is this really boast worthy?
We are the ones who teach that anyone can believe the gospel. Why would we boast in doing something anyone is able to do?
It’s the Calvinists who believe this ability is uniquely given to them and not most people. It makes much more sense for a Calvinist to boast in an ability granted to him that has been withheld from most others.
A great singer, for example, is a given a rare gift from birth and can often become proud or boastful due to that unique gift. But if everyone was born able sing that well whenever they wanted, then boasting in that ability would not make any sense. Thus, Calvinism leaves more room for boasting than does our soteriological perspective. (Though I don’t believe true Christians from either soteriological system would boast in such things: SEE HERE)
This speaks to the biblical teaching on the attainability of goodness or righteousness, which we will discuss in the next point.
4) A Decision Does Not Merit Salvation:
What is the underlying motivation for asking the question, “Why you and not another?” The implication seems to be that one who makes the libertarianly free decision to accept the gospel appeal is meriting or more deserving of salvation? As if the decision to repent somehow earns or merits one’s forgiveness.
Think of it this way. Did the prodigal son earn, merit or in any way deserve the reception of his father on the basis that he humbly returned home? Of course not. He deserved to be punished, not rewarded. The acceptance of his father was a choice of the father alone and it was ALL OF GRACE. The father did not have to forgive, restore and throw a party for his son on the basis that he chose to come home. That was the father’s doing.
Humiliation and brokenness is not considered “better” or “praiseworthy” and it certainly is not inherently valuable. In fact, one could argue that it was weak and pitiful of the son to return home and beg his daddy for a job instead of working his own way out of that pig sty. The only thing that makes this quality “desirable” is that God has chosen to grace those who humble themselves, something He is in no way obligated to do (Is. 66:2). God gives grace to the humble not because a humble response deserves salvation, but because He is gracious.
Calvinists often conflate man’s choice to confess with God’s choice to forgive while labeling it all “salvation.” They go on to convincingly argue that God is “sovereign over salvation” which actually means “God is as much in control over His own choice to forgive as He is over man’s choice to confess in faith.” It’s difficult to argue with someone who is making the case that God is “in control of salvation” and is “the One who gets all credit for salvation,” but that difficulty only exists due to the conflating of man’s responsibility to believe/confess with God’s gracious choice to save whosoever does so. Of course Salvation is all of God, but that is distinct from man’s responsibility to humbly trust in Him for salvation.
We all affirm that Salvation belongs to the Lord, but that does not mean sin and the responsibility to repent from sin does not belong to the sinner.
Clearly scripture calls us to humility and there is nothing which suggests we cannot respond in humility when confronted by the powerful clear revelation of God’s convicting life-giving truth through the law and the gospel. Consider what our Lord taught us in Luke 18:10-14
“Two men went up into the temple to pray, one a Pharisee and the other a tax collector. “The Pharisee stood and was praying this to himself: ‘God, I thank You that I am not like other people: swindlers, unjust, adulterers, or even like this tax collector. ‘I fast twice a week; I pay tithes of all that I get.’ “But the tax collector, standing some distance away, was even unwilling to lift up his eyes to heaven, but was beating his breast, saying, ‘God, be merciful to me, the sinner!’ “I tell you, this man went to his house justified rather than the other; for everyone who exalts himself will be humbled, but he who humbles himself will be exalted.”
Did the tax collector deserve to go home justified because of his humble admission of guilt? Of course not. If that were so, then his confession would have merited his salvation and there would be no reason for Christ’s death to atone for his sin. He went home justified because of God’s grace and provision alone! Maintaining man’s libertarianly free responsibility to repent and believe does not negate the truth that salvation is completely and totally of God alone.
Throughout the scriptures we see examples of God “finding favor” in believing individuals (Job, Enoch, Noah, Abram, etc), but these men, like all of humanity, still fell short of God’s glory and were unrighteous according to the demands of God’s law. They needed a savior. They needed redemption and reconciliation. Even those who believe the truth of God’s revelation deserve eternal punishment for their sin.
What must be understood is that no one was righteous according to the demands of the law. However, that does NOT mean that all people are unable to believe God’s revealed truth so as to be credited as righteous by God’s grace. Paul taught that no one was righteous in Romans 3, yet he turns around and declares in the very next chapter that, “Abraham believed God, and it was credited to him as righteousness” (4:3).
How can that be? Has Paul contradicted himself? First he declares that no one is righteous and then he tells us that Abraham was righteous? Which is it?
Paul is drawing the distinction between righteousness by works (Rm. 3:10-11) and righteousness by grace through faith (Rm. 3:21-24). The former is unattainable but the latter has always been very much attainable by anyone, which again, is why ALL ARE “WITHOUT EXCUSE!” (Rm. 1:20)
God can show mercy on whom ever he wants to show mercy! We happen to know, based on Biblical revelation, that God wants to show mercy to those who humbly repent in faith, which is man’s responsibility not God’s!
If you wait on God to effectually humble you, it will be too late.
1 Peter 5:5-6: “God opposes the proud but shows favor to the humble.” Humble yourselves, therefore, under God’s mighty hand, that he may lift you up in due time.
Isaiah 66:2: “These are the ones I look on with favor: those who are humble and contrite in spirit, and who tremble at my word.
James 4:10: “Humble yourselves before the Lord, and he will lift you up.”
2 Kings 22:19: “Because your heart was responsive and you humbled yourself before the Lord when you heard what I have spoken against this place and its people—that they would become a curse and be laid waste—and because you tore your robes and wept in my presence, I also have heard you, declares the Lord.”
2 Chronicles 12:7: When the Lord saw that they humbled themselves, this word of the Lord came to Shemaiah: “Since they have humbled themselves, I will not destroy them but will soon give them deliverance. My wrath will not be poured out on Jerusalem through Shishak.
2 Chronicles 12:12: Because Rehoboam humbled himself, the Lord’s anger turned from him, and he was not totally destroyed.
Psalm 18:27: You save the humble but bring low those whose eyes are haughty.
Psalm 25:9: He guides the humble in what is right and teaches them his way.
Psalm 147:6: The Lord sustains the humble but casts the wicked to the ground.
Proverbs 3:34: He mocks proud mockers but shows favor to the humble and oppressed.
Zephaniah 2:3: Seek the Lord, all you humble of the land, you who do what he commands. Seek righteousness, seek humility; perhaps you will be sheltered on the day of the Lord’s anger.
Matthew 18:4: Whoever humbles himself like this child is the greatest in the kingdom of heaven.
Matthew 5:3: Blessed are the poor in spirit, for theirs is the kingdom of heaven.
Matthew 23:12: For those who exalt themselves will be humbled, and those who humble themselves will be exalted.
Luke 1:52: He has brought down rulers from their thrones but has lifted up the humble.
Luke 14:11: For all those who exalt themselves will be humbled, and those who humble themselves will be exalted.”
Luke 18:14: “I tell you that this man, rather than the other, went home justified before God. For all those who exalt themselves will be humbled, and those who humble themselves will be exalted.”
James 4:6: But he gives us more grace. That is why Scripture says: “God opposes the proud but shows favor to the humble.”
The Bible Brodown guys discuss this question HERE in a great podcast.
 John Piper said, “More specifically, I rarely meet Christians who want to take credit for their conversion. There is something about true grace in the believer’s heart that makes us want to give all the glory to God. So, for example, if I ask a believer how he will answer Jesus’s question at the last judgment, “Why did you believe on me, when you heard the gospel, but your friends didn’t, when they heard it?” very few believers answer that question by saying: “Because I was wiser or smarter or more spiritual or better trained or more humble.” Most of us feel instinctively that we should glorify God’s grace by saying: “There but for the grace of God go I.” In other words, we know intuitively that God’s grace was decisive in our conversion. That is what we mean by irresistible grace.” (http://www.desiringgod.org/articles/what-we-believe-about-the-five-points-of-calvinism#Grace)
 Libertarian Free Will is “the categorical ability of the will to refrain or not refrain from a given moral action.” See: https://soteriology101.com/2016/05/11/philosophical-reflections-on-free-will/
 Question begging is the logical fallacy of presuming true the very argument up for debate. By asking what determined a man’s choice, the questioner is presuming someone or something other than that man made the determination, thus presuming true the foundation for deterministic logic (i.e. “a theory or doctrine that acts of the will, occurrences in nature, or social or psychological phenomena are causally determined by preceding events or natural laws [or Divine decree].” Merriam-Webster Dictionary). While a determiner may state reasons or influential factors for his or her own determination (i.e. I chose to overeat because it tastes so good) that does not mean the factors listed effectually caused the determination (i.e. the taste of food determined the agent’s choice to overeat). The agent alone made the determination based on the factors taken into consideration and deliberated upon. To presume without proof that something or someone outside the agent himself made the determination (i.e. was the “decisive factor”) is question begging.
 On the one hand, Calvinists argue that mankind always chooses according to their greatest inclination which is ultimately determined by their God given nature, yet on the other hand they affirm that Adam “was perfectly free from any corruptions or sinful inclinations,” and that he “had no sinful inclinations to hurry him on to sin; he did it of his own free and mere choice” Jonathan Edwards, ‘All God’s Methods Are Most Reasonable’, in Sermons and Discourses: 1723-1729, ed. by Kenneth P. Minkema, Works 14 (1997): 168.)
How does the affirmation of Adam’s freedom to sin or refrain from sin not violate the Calvinists own definition of human will and choice? For Adam to choose to sin he must violate the law of his own nature, as defined by the Calvinistic systematic.
 RC Sproul, Chosen By God, p.31
 John Calvin, “The Eternal Predestination of God,” 10:11