Flaw

A Flaw, is a problem, a fault, a mar. In other words, it is something that makes anything not perfect.

Often, a Mary Sue will either have no flaws at all, or have so many that everything she is doing is completely impossible for someone as theoretically messed up as she is.

But, on the other hand, human beings as a whole are so fantastically flawed it is a wonder we manage to do anything at all.

It's just best not to think too much on the subject of flaws, unless it is on the topic of characterization or jewelery.