How does a speaker blow out?

I don't understand how a speaker "blows" if the wattage of the amplifier is less than the upper limit of the speaker's limit.  Then again, I guess I don't really understand what "clipping" is.  The amp is 22w, I was listening at a moderately high level, there was a bass heavy section in the music, and then I heard the most painful noise coming from one the of woofers.  Sad.