I've found in my life if I tell myself I am capable, smart, strong etc. I become those things. It is not "the secret" it's the truth and really I think it's, in a way, showing my Heavenly Father gratitude for the body/ mind He has given me by being positive with myself.
I tell my kids all the time "you become what you think" and here I was "thinking" that I was incapable. So it hit me one day, I CAN do those things. I may not be GOOD at them but the only way to get good at them is to keep doing it!