Learn to be a great investor  reading a lot
A QUESTION Warren Buffett and Charlie Munger are often asked is: how do you learn to be a great investor?

“First of all,” says Charlie Munger, “you have to understand your own nature. Each person has to play the game given his own marginal utility considerations and in a way that takes into account his own psychology. If losses are going to make you miserable — and some losses are inevitable — you might be wise to utilise a very conservative pattern of investment and saving all your life. So you have to adapt your strategy to your own nature and your own talents. I don’t think there’s a onesizefitsall investment strategy that I can give you."

“Next”, says Munger, “you have to gather information. I think both Warren and I learn more from the great business magazines than we do anywhere else. It’s such an easy, shorthand way of getting a vast variety of business experience just to rifle through issue after issue covering a great variety of businesses. And if you get into the mental habit of relating what you’re reading to the basic structure of the underlying ideas being demonstrated, you gradually accumulate some wisdom about investing. I don’t think you can get to be a really good broadrange investor without doing a massive amount of reading. I don’t think any one book will do it for you."

Nor should reading be random: “… you have to have some idea of why you’re looking for the information. Don’t read annual reports the way Francis Bacon said you do science — which, by the way, is not the way to do science — where you just collect endless data and then only later do you try to make sense of it. You have to start with some ideas about reality. And then you have to look to see whether what you’re seeing fits in with proven basic concepts.

“Frequently, you’ll look at a business having fabulous results. And the question is, ‘How long can this continue?’ Well, there’s only one way I know to answer that. And that’s to think about why the results are occurring now — and then to figure out what could cause those results to stop occurring."

“On the other hand,” says Charlie, “if it weren’t a little difficult, everybody would be rich."

(from Buffett’s 1965 letter to Partners)
Diversification
Last year in commenting on the inability of the overwhelming majority of investment managers to achieve performance superior to that of pure chance, I ascribed it primarily to the product of: "(1) group decisions  my perhaps jaundiced view is that it is close to impossible for outstanding investment management to come from a group of any size with all parties really participating in decisions; (2) a desire to conform to the policies and (to an extent) the portfolios of other large wellregarded organizations; (3) an institutional framework whereby average is "safe" and the personal rewards for independent action are in no way commensurate with the general risk attached to such action; (4) an adherence to certain diversification practices which are irrational; and finally and importantly, (5) inertia.”
This year in the material which went out in November, I specifically called your attention to a new Ground Rule reading, "7. We diversify substantially less than most investment operations. We might invest up to 40% of our net worth in a single security under conditions coupling an extremely high probability that our facts and reasoning are correct with a very low probability that anything could drastically change the underlying value of the investment."
We are obviously following a policy regarding diversification which differs markedly from that of practically all public investment operations. Frankly, there is nothing I would like better than to have 50 different investment opportunities, all of which have a mathematical expectation (this term reflects the range of all possible relative performances, including negative ones, adjusted for the probability of each  no yawning, please) of achieving performance surpassing the Dow by, say, fifteen percentage points per annum. If the fifty individual expectations were not intercorrelated (what happens to one is associated with what happens to the other) I could put 2% of our capital into each one and sit back with a very high degree of certainty that our overall results would be very close to such a fifteen percentage point advantage.
It doesn't work that way.
We have to work extremely hard to find just a very few attractive investment situations. Such a situation by definition is one where my expectation (defined as above) of performance is at least ten percentage points per annum superior to the Dow. Among the few we do find, the expectations vary substantially. The question always is, “How much do I put in number one (ranked by expectation of relative performance) and how much do I put in number eight?" This depends to a great degree on the wideness of the spread between the mathematical expectation of number one versus number eight.” It also depends upon the probability that number one could turn in a really poor relative performance. Two securities could have equal mathematical expectations, but one might have .05 chance of performing fifteen percentage points or more worse than the Dow, and the second might have only .01 chance of such performance. The wider range of expectation in the first case reduces the desirability of heavy concentration in it.
The above may make the whole operation sound very precise. It isn't. Nevertheless, our business is that of ascertaining facts and then applying experience and reason to such facts to reach expectations. Imprecise and emotionally influenced as our attempts may be, that is what the business is all about. The results of many years of decisionmaking in securities will demonstrate how well you are doing on making such calculations  whether you consciously realize you are making the calculations or not. I believe the investor operates at a distinct advantage when he is aware of what path his thought process is following.
There is one thing of which I can assure you. If good performance of the fund is even a minor objective, any portfolio encompassing one hundred stocks (whether the manager is handling one thousand dollars or one billion dollars) is not being operated logically. The addition of the one hundredth stock simply can't reduce the potential variance in portfolio performance sufficiently to compensate for the negative effect its inclusion has on the overall portfolio expectation.
Anyone owning such numbers of securities after presumably studying their investment merit (and I don't care how prestigious their labels) is following what I call the Noah School of Investing  two of everything. Such investors should be piloting arks. While Noah may have been acting in accord with certain timetested biological principles, the investors have left the track regarding mathematical principles. (I only made it through plane geometry, but with one exception, I have carefully screened out the mathematicians from our Partnership.)
Of course, the fact that someone else is behaving illogically in owning one hundred securities doesn't prove our case. While they may be wrong in overdiversifying, we have to affirmatively reason through a proper diversification policy in terms of our objectives.
The optimum portfolio depends on the various expectations of choices available and the degree of variance in performance which is tolerable. The greater the number of selections, the less will be the average yeartoyear variation in actual versus expected results. Also, the lower will be the expected results, assuming different choices have different expectations of performance.
I am willing to give up quite a bit in terms of leveling of yeartoyear results (remember when I talk of “results,” I am talking of performance relative to the Dow) in order to achieve better overall longterm performance. Simply stated, this means I am willing to concentrate quite heavily in what I believe to be the best investment opportunities recognizing very well that this may cause an occasional very sour year  one somewhat more sour, probably, than if I had diversified more. While this means our results will bounce around more, I think it also means that our longterm margin of superiority should be greater.
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