Sheep, lemmings, etc.

"People are faced with too many options, in this case 48 songs. Since you can't listen to all of them, a natural shortcut is to listen to what other people are listening to," Salganik said. "I think that's what happens in the real world where there's a tremendous overload of songs."

Alternatively, Salganik said, a desire for compatibility with others could drive the choice, since much of the pleasure from listening to music and reading books stems from discussing them with friends.