Earnings season is an emotional time on Wall Street, and I think it's the perfect time to revisit Ben Graham's famous description of "Mr. Market."

Ben Graham was Warren Buffett's business school professor. Graham wrote several books explaining how he thought about the markets, and in one of those books, he compared the market's price swings to the lunatic ravings of Mr. Market. In Graham's description, when Mr. Market is happy, he will bid the price of stocks up. But suddenly and often for no apparent reason, Mr. Market will fall into a deep fit of despair. Then he wants to sell all of his holdings at low prices, and he won't take no for an answer.