I have a couple of great books on this very subject. A classic story is this:

Julian Lennon calls up Paul McCartney (his surrogate Dad) because John was being mean to him and he was sad.

Paul picked him up and spent some time being a surrogate Dad and then wrote a song called Hey Jules to make Julian feel better.

He later changed the titled to Hey Jude.

John heard it and said.

"That's the best song you have ever written Paul. Is about me?"