I think Lewis said it himself once.."This is the hevyweight division anybody can get knocked out if they are caught"

Don't remember if those were his exact words but the point is. When you are fighting guys who weigh over 220 pounds, you better alwais be on your toes, because it only takes one good shot.

My opinion is, he did not have a glass chin. He just was not 100% focussed as he should have been in a HW title fight.