Antigone's fierce devotion is once more on full display when she declares that she'll bury Polyneices despite Creon's law. It is this rebellious act and Antigone's determined loyalty to the memory of her brother that forms the spine of the play. Her stubborn loyalty becomes her hamartia , her tragic error, and ultimately causes her downfall. Antigone is a great example of how a hamartia doesn't necessarily have to be a character "flaw" as it is often described. Most people would call loyalty an admirable trait. Antigone's devotion is so extreme, however, that it brings tragedy once more to Thebes.
It is also significant to note Aristotle's delineation of the tragic hero's character. The tragic hero is not an eminently 'good' man, or model of virtue swiftly brought down by adversity. In that, says Aristotle, there is only shock - since we can see none of ourselves in a perfectly virtuous man, and find it arbitrary that he would be selected for cosmic punishment. What is far more effective is if the hero possesses some 'frailty', or flaw (like Achilles' heel), which he compensates for, hides, runs away from - but eventually catches up with him. An 'error' of character should not be confused with an error in a character's 'action' - a tragedy must spin on a fundamental flaw in the hero's behavior and one that the audience can identify with or substitute in themselves. Only through the tragic climax can he - and the audience - find redemption.