He got hurt badly and rocked all over the place by Gray Maynard. Gray Maynard has 2 ko's in 20 fights and both were over complete nobodies. You could make the argument that Aldo has a better chin since he was able to survive getting hit clean by Mendes several times. He took Cub down and controlled him, tko'd Mendes early etc... I'm not saying he has a bad chin but he's considered to have one of the best chin's in the history of mma yet he hasn't really been hit clean by any ko artists.