What reason might there be for the claim that it would be logical to find a Calvinist who was convinced he was one of the damned (non-elect)?

I ask due to a comment to this old question https://christianity.stackexchange.com/questions/33767/according-to-calvinism-why-does-god-give-mercy-to-some-and-not-to-others/33768#33768 Under the answer by a Calvinist that got 16 up-votes and the Green Tick, a person asked, “Has anyone ever encountered a Calvinist who was convinced he was one of the damned (non-elect)? Logically, such people ought to exist.” Another commentator said, Yes, he had had considerable dealings with just such a (miserable) person, concluding, “He somehow misinterpreted the so-called 'doctrines of grace' to be doctrines of condemnation.” I maintain this question is unique on Stack because it does not ask what God’s view, or the Bible’s view might actually be on ‘election’ unto salvation, but seeks to understand how individuals accepting that might arrive at the conclusion that they had not freely received God’s mercy. **This question is addressed to Calvinists** who might understand experientially the dilemma of someone self-identifying as a Calvinist, yet who is convinced they were damned (not elected by the grace of God unto salvation, in other words).