we have to remember that if our competitors changed, enhanced or optimized there site OR got some pretty decent backlinks that might make them drop too...
So Joe Blow selling candy canes is in the 5th spot, he then does some fancy
SEO and gets about 6 quality links back to his site and suddenly the engines "like his site better" (so to speak) and he get's the top spot, well that just might bump you down a few notches or so...