I want to say something really profound about art or collaboration, or somehow tie this into writing, but I'm just too freaking wowed by it. Check this out.
Basically, it's an excerpt from a BBC special pulling apart some songs from Sgt. Pepper, and a few from other albums. They've separated the tracks, so you can hear each Beatle's individual contribution to a song, and how George Martin tied everything together so beautifully. Really worth a listen.