When legendary investor Warren Buffett was asked what the best money advice he ever received, he replied referencing “by far the best book on investing ever written,” The Intelligent Investor, written in 1949 by Benjamin Graham.
Buffett was a student of Graham's at Columbia and subsequently worked for him before breaking off on his own.
“Chapters 8 and 20 have been the bedrock of my investing activities for more than 60 years,” he says. “I suggest that all investors read those chapters and reread them every time the market has been especially strong or weak.”
So what's the core of these two chapters?
The Investor and Market Fluctuations
Buffett explains in his 1987 letter to shareholders:
Ben Graham, my friend and teacher, long ago described the mental attitude toward market fluctuations that I believe to be most conducive to investment success. He said that you should imagine market quotations as coming from a remarkably accommodating fellow named Mr. Market who is your partner in a private business. Without fail, Mr. Market appears daily and names a price at which he will either buy your interest or sell you his.
Without fail, Mr. Market appears daily and names a price at which he will either buy your interest or sell you his.
Even though the business that the two of you own may have economic characteristics that are stable, Mr. Market's quotations will be anything but. For, sad to say, the poor fellow has incurable emotional problems. At times he feels euphoric and can see only the favorable factors affecting the business. When in that mood, he names a very high buy-sell price because he fears that you will snap up his interest and rob him of imminent gains. At other times he is depressed and can see nothing but trouble ahead for both the business and the world. On these occasions he will name a very low price, since he is terrified that you will unload your interest on him.
Mr. Market has another endearing characteristic: He doesn't mind being ignored. If his quotation is uninteresting to you today, he will be back with a new one tomorrow. Transactions are strictly at your option. Under these conditions, the more manic-depressive his behavior, the better for you.
But, like Cinderella at the ball, you must heed one warning or everything will turn into pumpkins and mice: Mr. Market is there to serve you, not to guide you. It is his pocketbook, not his wisdom, that you will find useful. If he shows up some day in a particularly foolish mood, you are free to ignore him or to take advantage of him, but it will be disastrous if you fall under his influence. Indeed, if you aren't certain that you understand and can value your business far better than Mr. Market, you don't belong in the game. As they say in poker, “If you've been in the game 30 minutes and you don't know who the patsy is, you're the patsy.
… [A]n investor will succeed by coupling good business judgment with an ability to insulate his thoughts and behavior from the super-contagious emotions that swirl about the marketplace. In my own efforts to stay insulated, I have found it highly useful to keep Ben's Mr. Market concept firmly in mind.
Margin of Safety as the Central Concept of Investment
The core of this idea to know what a business is worth and pay less.
Again Buffett explains in his own words. At the 1997 annual meeting, Buffett explains this concept (quoted from Andrew Kilpatrick's, Of Permanent Value: The Story of Warren Buffett)
If you understood a business perfectly and the future of the business, you would need very little in the way of a margin of safety. So, the more vulnerable the business is, assuming you still want to invest in it, the larger margin of safety you'd need. If you're driving a truck across a bridge that says it holds 10,000 pounds and you've got a 9,800 pound vehicle, if the bridge is 6 inches above the crevice it covers, you may feel okay, but if it's over the Grand Canyon, you may feel you want a little larger margin of safety.
When Mr. Market is happy he can materially erode the “margin of safety” that is the cornerstone of Buffett and Graham's approach to investing.