Explain this saying “You cannot win someone else's race”.

So, basiclly, its saying that if someone like a friend or family etc; has something going on, like a law accusation or sum, you can try to help, but you cant do it for them.    

you see what im sayin? i know what it means but like, i cant explain it very well, hope this helpppsss!

"why don't you like me the way i am? " i cried. "i'm not a genius! i can't play the piano, and even if i could, i wouldn't go on tv if you paid me a million dollars! "

explanation:

the conflict between jing-mei and her mother is over jing-mei's piano lessons since her mother wants her to become a prodigy but she does not want to play it any more.