I think that if you start worrying about it, you've already lost the game.
"I think that if you start worrying about it"＝「それについて気にし始めたら」
"you've already lost the game"＝「既に試合に負けたことになると思うから」
★この"game"は比喩として使っていますが、文脈によって相手にはそれは通じると思います。
Example in context:
"Just remain confident about it. Don't worry or care much about it, because otherwise, you've already lost the game."
アメリカ合衆国 
