Self-doubt comes from you guessed it yourself. The world has countless opportunities waiting just for you. Have you ever went to a vending machine and saw the sign broken? Would you deposit money into the machine expecting anything in return? Of course not because it is broken.
Oftentimes God cannot deposit into people the things He desires for us until we are ready. No one is perfect however we should be continually working on becoming the best version of ourselves. Make one small step today towards your vision.