"Let sleeping dogs lie"

The idiom let sleeping dogs lie means not to stir up old conflicts or provoke an argument over unresolved issues. It is often better to agree to disagree and move forward rather than trigger hostilities over an ongoing difference of opinion. Let sleeping dogs lie refers to the instinctive behavior of a dog whenever it is awakened suddenly from a nap. Many dogs instinctively lash out at those who try to awaken them without reason, and these natural responses are often quite painful.