主語從句中存在三個語法錯誤：（1）引導詞重疊（that whether）；（2）缺少主語；（3）冠詞問題（ability前應該有定冠詞the）.
建議改為以下的一種：
1 The difference between the winners and the losers is that the former has the ability to solve problems, while the latter doesn't have it.
2 Whether a person has the ability to solve problems determines whether he is a winner or a loser.
3 The difference between the winner and the loser lies in the ability or inability to solve problems.
4 The ability to solve problems differentiates the winners from the losers.