In Poetics 13, Aristotle claims that the protagonist in the most beautiful tragedies comes to ruin through some kind of ‘failure’—in Greek, ἁμαρτία. There has been notorious disagreement among scholars about the moral responsibility involved in ἁμαρτία. This article defends the old reading of ἁμαρτία as a character flaw, but with an important modification: rather than explaining the hero's weakness as general weakness of will (ἀκρασία), it argues that the tragic hero is blinded by temper (θυμός) or by a pursuit for fine, good and desirable things—that is, by what may be labelled ‘qualified’ weakness of will. The upshot is that ἁμαρτία ends up as being less blameworthy than ‘proper’ ἀκρασία, but still explains why morally outstanding people are unsuitable for the most beautiful tragedies.