Why are some people so talented?

I love acting and music, and I sometimes trick myself into thinking that I am alright at them. But then I'll see my 16 year old friend- who is an incredible artist, a singer of operatic standards, a great dancer, and when she acts, people cry- and my self esteem plummets. She says that being talented sucks, and that it' always been a part of her life. So I want to get your insight, how do we determine if someone is talented, and what causes them to be so? Is it their childhood, or hereditary, or something deeper, more coincidental?