Can't is a strong word. Think of how many times you had a thought and immediately followed with, "I can't." And there it ends. All your talent — all your potential — wasted.
Figure out why you default to this type of self-defeating behavior. Stop allowing this to happen. To put it another way, get 't-d' off. (Get it? Take the 't' off the word 'can't' to make it the word 'can'.)
If you need anything, just email me. I'm always here to help.