Hamartia
The flaw, error, or misjudgment that brings about a tragic hero’s downfall.
Hamartia is the crack in an otherwise great character—sometimes a moral weakness, sometimes a simple mistake—that leads to catastrophe. Writers use it to make a downfall feel motivated rather than arbitrary. It ties the hero’s suffering to their own nature or choices.
Example
Othello’s readiness to believe the worst, his consuming jealousy, is the flaw Iago exploits to steer him toward disaster.
Othello · William Shakespeare