Looking at it from a parents view, I have 5 kids, I would say this. It is the responsibility of the parent to put their children in positions where they can have success, which in turn will add to their self esteem. Some kids however are naturally blessed with more of it than others, so it especially crucial to reinforce the positive behaviors and successes of children who don't naturally possess it. There is no single answer to this as they are all inheritently different. My most successful child who is the most athletic and accomplished is not as self confident as you would expect. He needs that positive reinforcement more. Another child who has a harder times with things is perfectly content to be who she is and doesn't need as much patting on the back.
I think the key though is to set appropriate goals for them, make sure they give their best effort, and compliment the effort vs. the result. THAT is what will bring them happiness. My wife likes to use the phrase "Bloom where you are planted". As was said before in this thread not everyone can do everything they choose. I'd sure like to be the starting PF for the Celtics, however my 6'1" frame and so-so athleticism don't really allow me to be "whatever I want to be".