Someone who keeps his nose to the grindstone works very hard. This can help a worker keep his nose clean or stay out of trouble.

keeps his nose to the grindstone是指人埋头苦干，工人这么做就是循规蹈矩(keep his nose clean)，会少了麻烦。

Jim had decided he was going to keep his nose to the grindstone.

【nose】吉姆下定决心努力工作。

Larry had a chance of getting in on the ground floor, and if he kept his nose to the grindstone he might well be many times a millionaire by the time he was forty.

拉里有机会进入底层，如果他坚持不懈地努力，到四十岁时他很可能成为百万富翁很多倍。