When you focus on what you can't do, you begin to amplify the feelings of "can't", instead focus on what you can do, and those too will begin to multiply. Even if you don't necessarily believe that you can do something whole heartedly, the more you say it to yourself, the more it will begin to shape your reality.
Your feelings are the way in which our subconscious mind really communicates with you. If your thoughts make you feel not so good about yourself, those thoughts need to be re-wired.
Once you have identified a few thought patterns that are no longer serving you, instead of getting caught up with them, change them. There is always a way to change these thoughts into ones that uplift and make you feel good.
"I can't do this because….."
Change it to:
"I am going to use my strengths and focus on what I can do rather than what I can't do."