"Rule No. 1: Never lose money. Rule No. 2: Never forget rule No. 1." - Warren Buffett With all due respect to Warren Buffett, the #1 rule in investing is not anything close to "never lose money." In fact, the entire notion is absurd. Anyone who has ever invested in the history of the world has lost money at one time or another. Buffett himself lost close to 50% on two separate occasions.