My weak spot is laziness. Oh, I have a lot of weak spots: cookies, croissants.
You look closely enough, you'll find that everything has a weak spot where it can break, sooner or later.
Truthfulness is a cornerstone in character, and if it be not firmly laid in youth, there will ever after be a weak spot in the foundation.
Everyone has their weak spot. The one thing that, despite your best efforts, will always bring you to your knees, regardless of how strong you are otherwise.
The whole key is to be honest with yourself, find the weak spots, work on it, get it done.
When a problem comes along, study it until you are completely knowledgeable. Then find that weak spot, break the problem apart, and the rest will be easy.