My favorite answer is by Adam Duritz of Counting Crows (starting at 4:44):
I think Lennon's a great lyricist especially … a great writer, really. But melody is unquantifiable. I mean, you live your day, so you've got shit to write about. I don't know where people get melody from. The ability to write something that sticks in people's heads for 10, 20, 50, couple hundred years — the ability to be Puccini or McCartney … I don't know where that comes from. And I don't know how one guy wrote so many pieces of music that I can hum 50 years later. I don't know how it's possible. And that to me is such a rare thing.… All the dark … cool songs in the world are great, but the only reason we love music is because melody gets to the gut.… The ability to write something that we're all humming … that's how I remember the Beatles. Not that Lennon didn't write a lot of great songs too, but McCartney's abilities there are … without peer.
