What is meant by the phrase let sleeping dogs lie?

Answer 1

Probably from a Latin proverb, 'Quieta non movere' meaning 'do not move settled things'. Also there is a quotation from the Book of Proverbs 'He that passes by and meddles with strife not belonging to him, is like one that takes a dog by the ears'. In other words, do not instigate trouble

Answer 2

The phrase let sleeping dogs lie is an English idiom that means that someone should just not interfere with things. One would use this phrase when one does not want to get involved with something.
'Let sleeping dogs lie', means for one to not disrupt a situation that is going well as it will lead to problems.

If that metaphorical dog is just laying there asleep, leave him be. Don't go messing with him or he might wake up and bite you. Of course if the dog is lying on a memory foam dog bed, he might not be bothered to wake up anyway.
The 'dog' here is whatever 'bone of contention'--or issue that will most likely only erupt into another conflict--that has been discussed once, and is now for the moment at least 'asleep.' It means to leave what will only become a problem alone so as to avoid the problem.
The phrase "let sleeping dogs lie" means to leave a situation alone or not to start trouble where there is not any already. The earliest use of the phrase is found in a French proverb which dates back to the 14th century.