Black Swan ending explained

What happens

Nina dances the Black Swan triumphantly, then finds that the wound she blamed on Lily is self-inflicted: she stabbed herself with glass. She still performs the White Swan's final leap and falls, bleeding, onto a mattress.

The last line

"I felt it. Perfect. It was perfect."

What it says

Nina finally becomes both swans, but the film refuses to reward her for it. Her perfectionism has been consuming her all along, so the only perfect performance is one she cannot survive.