If a more deadly flaw is chosen, it must be well motivated. In the villain, this flaw is a vice carried to extremes. In both cases, the fatal flaw is the trait that has the potential to bring about the character's downfall. The 80's movie Scarface had a focal character who was also the villain, and it was his addiction to cocaine that brought about his demise. More recently, Pulp Fiction featured a scheming and ruthless boxer played by Bruce Willis, and while he was never brought down, his fatal flaw of over-confidence combined with his shadow and put him very close.
Fatal flaws are always consistent with the spine and supporting trait.
If not, you've got yourself a neurotic or even psychotic character. Although this might be appropriate in some cases, it isn't something you want to introduce accidentally. Thus an ambitious entrepreneur might have a supporting trait of being organized and a fatal flaw of being hot-tempered., but not a supporting trait of hanging out with the guys or a fatal flaw of timidness. Edward's fatal flaw is his need for revenge against a wealthy father who deserted his mother and him and failed to support them. It's important to notice that Edward's anger is as much in his mother's behalf as his own, which gives a more sympathetic tone to his goal.