Mr. Market is an allegory created by investor Benjamin Graham. Graham asks the reader to imagine that he is one of the two owners of a business, along with a partner called Mr. Market. The partner frequently offers to sell his share of the business or to buy the reader's share. This partner is what today would be called manic-depressive, with his estimate of the business's value going from very pessimistic to wildly optimistic. The reader is always free to decline the partner's offer, since he will soon come back with an entirely different offer.
Since its introduction in Graham's 1949 book The Intelligent Investor, it has been cited many times to explain that the stock market tends to fluctuate. The example makes it clear that the sole reason for the change in price is Mr. Market's emotions. A rational person will sell if the price is high and buy if the price is low. He would not sell because the price has gone down or buy because the price has gone up. Graham instead believes that it is important to focus on whether the stock valuation of a company is reasonable after calculating its value through fundamental analysis. Warren Buffett has been quoted numerous times on Graham's 1949 book The Intelligent Investor. Chapter eight covers Mr. Market and Warren Buffett thinks that this is the best part of the book.  Buffett described it as "by far the best book on investing ever written".
Mr. Market is often identified as having human behavioral manic-depressive characteristics, it:
- Is emotional, euphoric, moody
- Is often irrational
- Offers that transactions are strictly at your option
- Is there to serve you, not to guide you.
- Is in the short run a voting machine, in the long run a weighing machine.
- Will offer you a chance to buy low, and sell high.
- Is ‘frequently efficient…but not always.
This behavior of Mr. Market allows the investor to wait until Mr.Market is in a 'pessimistic mood' and offers low sale price. The investor has the option to buy at that low price. Therefore patience is such an important virtue when dealing with Mr. Market.