Quote from bwolinsky:
No one ever tells you when to get back in. It's a cliche because while this anomally does happen regularly, it seems everyone just assumes you got back in at the low. No one has come up with any other axiom to re-enter.
On the other hand, witness Jim Cramer and other lunatic "financial analysts". They're never shy about telling you when to load up but they never once mention when you should unload.