Every fighter has one. Calzaghe was terrific but wanted no part of Robin Reid again (himself not a great fighter) as he got out of the that one by the skin of his nose and Hopkins made him look pretty bad though that's what Bernard does.
Of course Roy hung around too long just like Chavez and everyone else meets their match eventually whether it be down to age, shape , motivation etc.
I think PBF might be different. The only 2 question marks are ODLH fight (close though I thought he won it myself) and the first Castillo fight (where I thought the Mexican was robbed blind though in fairness to Floyd he dominated him in the rematch.)
JMM was far too small, 36, coming up 2 weights and looked really thick around the waist. IMHO he just shouldn't have been in there considering the disadvantages against a natural master like Floyd. Pac Man, Cotto and Mosley should provide vastly sterner challenges but I still see Floyd slickly outboxing all of them in cautious displays just like he did against Judah.
But Williams........mmmmmm. I guess we'll never know.