Encore!?

During a festive evening at the Oasis show, my dearest pal Amy began reflecting upon the nature of encores, as Noel had just said the previous song was their last. Yet they were back. Amid plumes of marijuana smoke, she surmised that they had obviously been lying, knowing full well that they would play in the extremely near future. When a band comes back out and plays an encore, there's a certain obligation the fan must feel to stay and listen.

This made it all the more exaspirating when Oasis began their encore with a song we'd never heard of. With a band like Oasis, if their last song isn't one that everyone knows, you can bet that there will be more songs to come. We both had to pee, and I had very quickly grown tired of Oasis. It was just time to go. Amy and I began to chant, "Sally Can Wait" with steady deliberation, knowing it was going to be the song that closed the half-set. But we were wrong. They did play "Sally," but it was not to be their last. They opted instead for an impromptu "My Generation," so that EVERYONE could sing along.

But why the encore? Is it an ego boost? Is it just common courtesy? Is it even necessary? How many shows have you been to that haven't ended with an encore?