Let sleeping dogs lie

Let sleeping dogs lie is an expression that refers to the condition of a sleeping dog when awakened. In most of the cases such dogs attack the person by whom they are awakened. This condition is applied in the human behaviour and thus it bemcame an idiom which means 'not to stir up those persons, conflicts, argument etc which are contentious or unresolved'.

There can be many examples. One of the popular example is of an ex-criminal who begins a normal life. People use this idiom as advice to all not to provoke that person or else such a person may return to his earlier behaviour or criminality.