Your child's self-esteem
Opinions on the best ways to learn differ, but all experts agree that children with a high level of self-esteem learn more easily and quickly than those with a poor self-image. "I can't do it. I'm too stupid" is a self-fulfilling prophecy. Raising a confident child starts with love, encouragement, and positive feedback. It also involves knowing your child (each is different) and being familiar with the stages of childhood development so that your expectations are realistic (what comes easily to a nine-year-old may be near impossible for a five-year-old). Criticism, even if it is only implied, is never helpful, and by all means avoid invidious comparisons ("Your sister Megan read 'Pride and Prejudice' when she was only nine!"). 
It is a good idea to encourage your child to try many things in order to discover where his talents lie. As he discovers what he likes and does well, he will work on these things and slowly gain competence. That competence is the key to a good self-image because (as we adults all know) competence leads to confidence!