A particular sin is a "finite amount." A lifetime of unrepentance is a "totality."
Wouldn't you say?
No I wouldn't A life is filled with many things, it's never pure "unrepentance".
And even if it were, that still doesn't address the issue of how it's "just" to have an eternal amount of punishment for, say, 50 years of "unrepentance". Maybe 50 years of punishment, perhaps, but not an infinite, unending amount for all eternity.
Furthermore, perhaps given another decade of life (or after the first decade of punishment), the "unrepentant" may well come to see the error of his earlier ways and achieve that instant of salvation which erases the rest -- where, then, is the justice in eternal punishment? There seems nothing "just" about that.