[bambax]

McCartney says in an interview about the early days of the Beatles that they used to compose and rehearse new songs in hotel rooms with no recording device or paper, and the goal was to be able to play the new songs the day after.

He says (quoting from memory): "if we couldn't remember our own songs how could we expect audiences to remember them?"

If a song is hard to remember it may have a hard time becoming a hit.