One must avoid the error of the preening duck that quacks boastfully after a torrential rainstorm

"In a bull market, one must avoid the error of the preening duck that quacks boastfully after a torrential rainstorm, thinking that its paddling skills have caused it to rise in the world. A right-thinking duck would instead compare its position after the downpour to that of the other ducks on the pond."

[Berkshire Hathaway Annual Report 1997]