Full Idea
It was possible at the start for the unjust and the intemperate person not to become like that, which is why such people are voluntarily unjust and intemperate; but once they have become like that, it is no longer possible not to be.
Gist of Idea
Depravity of character is initially voluntary, but eventually it can't be changed
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1114a20)
A Reaction
This seems to be generally true, but there seem to be cases of big changes later on in moral character, usually resulting from traumatic events. Or there may be a long slow progress into either depravity or nobility of character.
Book Reference
Aristotle: 'Nicomachean Ethics', ed/tr. Reeve, C.D.C. [Hackett 2024], p.44