some people don't know when to quit
some people (just) don't know when to quit
Said of someone who continues to engage in some action or activity after they have no hope of succeeding or are making things worse for themselves. A: "She keeps throwing money away on these failing investments. It's like she can't understand that they're never going to perform the way she wants." A: "Yeah, some people don't know when to quit." I told him to stop arguing with the boss like that, or he was going to get into even more trouble. Some people just don't know when to quit.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
some people (just) don't know when to quitand some people (just) don't know when to give up; some people (just) don't know when to stop
1. You, or someone being talked about, should stop doing something, such as talking, arguing, scolding, etc. (often directed toward the person being addressed.) Bill: I hate to say it again, but that lipstick is all wrong for you. It brings out the wrong color in your eyes, and it makes your mouth larger than it really is. Jane: Oh, stop, stop! That's enough! Some people just don't know when to quit. John: Those bushes out in the backyard need trimming. Sally: You keep criticizing! Is there no end to it? Some people don't know when to stop!
2. Some people do not know when to slow down and stop working so hard. Jane: He just kept on gambling. Finally, he had no money left. Sally: Some people don't know when to quit.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.