The key is having more information than the other guy – then analysing it right and using it rationally. - Warren Buffett

My old boss, Ben Graham, told me very early on you get more trouble with a good idea than a bad idea, because the good idea works. I mean, it's a good idea to buy a home, for example. And then people go crazy sometimes. The good idea works, and it works, and it works. Stocks work out better than bonds most of the time. And, after a while, people forget that there were some other limiting conditions. With Edgar Lawrence Smith's book, it was that when bonds yield the same as stocks — which was the case then — the stocks are going to outperform because they have this retained earnings. So stocks started going up in the Twenties and all of a sudden they were selling at 5 or 6 times the prices as when they bought the book. And the original correct perception on his part had experienced changing conditions, but people ... got their confirmation through stock prices. That's what happens in bull markets. People start out thinking stocks are cheap, and then they start thinking stocks have gone up. And, a stock can be a good buy or a bad buy. A bond can be a good buy or a bad buy. It depends on price.

Despite our policy of candor, we will discuss our activities in marketable securities only to the extent legally required. Good investment ideas are rare, valuable and subject to competitive appropriation just as good product or business acquisition ideas are.

The most common cause of low prices is pessimism — some times pervasive, some times specific to a company or industry. We want to do business in such an environment, not because we like pessimism but because we like the prices it produces. It's optimism that is the enemy of the rational buyer.