better left unsaid
[refers to a topic that] should not be discussed; [refers to a thought that] everyone is thinking, but would cause difficulty if talked about in public. (A typical beginning for this phrase might be It is, That is, The details are, or even Some things are. See the examples.) Mary: I really don't know how to tell you this. Bob: Then don't. Maybe it's better left unsaid. Bill: I had such a terrible fight with Sally last night. I can't believe what I said. Bob: I don't need to hear all about it. Some things are better left unsaid.