If you dont work hard, you may fail. 此句中fail意为失败;不及格,没有通过考试。fail还有其它用法。如:

　　① He never fails to write to his mother every week.

　　（fail意为忘记、忽视或未能做某事。）

　　② She has been failing in health.

　　（fail in意为（健康状况）衰退。）

　　③ His friends failed him when he most needed them.

　　（fail意为使失望, 辜负。）

　　④ I had three passes and one fail.

　　（fail用作名词,意为考试不及格。）

　　⑤ Ill be there at two oclock without fail.

　　（without fail意为肯定,一定,必定。）