Jason Zweig in a Wall Street Journal blog entry quotes many luminaries on their investment philosophy in 10 words or less (link1). Bogleheads on the Vanguard forum did theirs (link2).
The one that comes to mind first is:
Buy straw hats in winter.
But that doesn't really sum up what I do in terms of trading or investing, nor is it particularly accurate. Another cliche on my mind of late is:
Regression to the mean.
(bet with the odds, not against them)
Another one from the Graham/Dodd school:
Rule 1: don't lose money
Rule 2: don't lose money
Rule 3: don't lose money
For gunslingers that like to do all in, all out moves on leverage, their motto might be:
Be bold and be right.
(Q: What if you are not right?)
You go down with the ship.
One quip that goes with that one:
There are old traders, and bold traders, but no old bold traders.