In case you can’t quite pin the nail on the head

This is from a video about a person describing a mental health condition to his doctor. The speaker said, “It’s helpful to get a recording in case you can’t quite pin the nail on the head.”  This is a mashup of “pin it down” (to establish or determine something concretely) and “hit the nail on the head” (to do exactly the right thing).  As the submitter said, certainly the game “pin the tail on the donkey” was probably on the speaker’s mind.  A big thanks to Jake A. Phillips for sending this one in!