What's "let sleeping dogs lie" mean? Is this an idiom?

Native speaker’s answer
Rebecca
Yes, "let sleeping dogs lie" is an idiom! It means to leave things as they are as to not cause a disturbance or disagreement. It's kind of like a warning. The idea is that dogs can't disturb or harm you if you let them sleep instead of getting their attention, and the same goes for situations and problems. Ex: I thought about complaining to the manager, but I decided to let sleeping dogs lie instead. Ex: Don't bring up the schedule again. It'll start an argument. It's best to let sleeping dogs lie.