hamartia

A character’s tragic mistake or flaw.

From wikipedia

Hamartia (Ancient Greek: άμαρτία) is used in Aristotle’s Poetics, where it is usually translated as tragic mistake or tragic flaw. There is debate as to what exactly hamartia means in Aristotle’s Poetics. The word, in Homeric Greek, refers to a warrior who has missed his mark. If an archer or a spear thrower misses, άμαρτες has occurred.