Richard Feynman quote

“I can live with doubt, and uncertainty, and not knowing. I think it’s much more interesting to live not knowing than to have answers which might be wrong.” -Richard Feynman

Starting with a qualitative search...

From The Small-Cap Advantage: How Top Endowments and Foundations Turn Small Stocks into Big Returns:

Most investment processes begin with quantitative elements like filters and screens. The qualitative work is often left for the latter stages, after suitable investment candidates have been identified. Investment processes are often structured in this quantitative-first order for two reasons. First, it is more convenient for the manager to reduce the size of the opportunity set to a more manageable list of companies. Second, institutional investors often demand a step-by-step process that can neatly illustrate the filtering of thousands of companies into a final portfolio. But convenience and marketing should not be the drivers of a robust investment process. Managers who understand the hidden dangers of screening and strict adherence to quantitative investment processes should instead start with the qualitative search for competitive advantage and management talent. By compiling a list of qualitatively superior companies first, and limiting valuation work to these, a small-cap manager prevents being drawn into seductively cheap subpar ideas.

Marcus Aurelius quote

From Meditations:

It never ceases to amaze me: we all love ourselves more than other people, but care more about their opinion than our own. If a god appeared to us—or a wise human being, even—and prohibited us from concealing our thoughts or imagining anything without immediately shouting it out, we wouldn’t make it through a single day. That’s how much we value other people’s opinions—instead of our own.

Ben Graham quote

From The Intelligent Investor:

Mathematics is ordinarily considered as producing precise and dependable results; but in the stock market the more elaborate and abstruse the mathematics the more uncertain and speculative are the conclusions we draw therefrom. In forty-four years of Wall Street experience and study I have never seen dependable calculations made about common-stock values, or related investment policies, that went beyond simple arithmetic or the most elementary algebra. Whenever calculus is brought in, or higher algebra, you could take it as a warning signal that the operator was trying to substitute theory for experience, and usually also to give to speculation the deceptive guise of investment.

Statistics and investing...

From Nassim Taleb in Fooled By Randomness:

If the science of statistics can benefit me in anything, I will use it. If it poses a threat, then I will not. I want to take the best of what the past can give me without its dangers. Accordingly, I will use statistics and inductive methods to make aggressive bets, but I will not use them to manage my risks and exposure. Surprisingly, all the surviving traders I know seem to have done the same. They trade on ideas based on some observation (that includes past history) but, like the Popperian scientists, they make sure the costs of being wrong are limited (and their probability is not derived from past data).

Peter Lynch quote

From Beating the Street:

Buying a cyclical after several years of record earnings and when the P/E ratio has hit a low point is a proven method for losing half of your money in a short period of time.

Bertrand Russell and uncertainty

"I think nobody should be certain of anything. If you’re certain, you’re certainly wrong because nothing deserves certainty. So one ought to hold all one’s beliefs with a certain element of doubt, and one ought to be able to act vigorously in spite of the doubt…. One has in practical life to act upon probabilities, and what I should look to philosophy to do is to encourage people to act with vigor without complete certainty." -Bertrand Russell

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John Maynard Keynes quote

"In chemistry and physics and other natural sciences the object of experiment is to fill in the actual values of the various quantities and factors appearing in an equation or a formula; and the work when done is once and for all. In economics that is not the case, and to convert a model into a quantitative formula is to destroy its usefulness as an instrument of thought." -J. M. Keynes

Marcus Aurelius quote

From Meditations:

Your three components: body, breath, mind. Two are yours in trust; to the third alone you have clear title.  

If you can cut yourself—your mind—free of what other people do and say, of what you’ve said or done, of the things that you’re afraid will happen, the impositions of the body that contains you and the breath within, and what the whirling chaos sweeps in from outside, so that the mind is freed from fate, brought to clarity, and lives life on its own recognizance—doing what’s right, accepting what happens, and speaking the truth—  

If you can cut free of impressions that cling to the mind, free of the future and the past—can make yourself, as Empedocles says, “a sphere rejoicing in its perfect stillness,” and concentrate on living what can be lived (which means the present) … then you can spend the time you have left in tranquillity. And in kindness. And at peace with the spirit within you.

Montaigne quote

"In order always to be learning something by communication with others (which is one of the finest schools there can be), I observe in my travels this practice: I always steer those I talk with back to the subjects they know best....For most often the opposite happens: each man chooses to hold forth on another man's occupation rather than his own, thinking that this is so much new reputation acquired....Thus we must always throw the architect, the painter, the shoemaker and the rest each back to his quarry. And apropos of this, in the reading of history, which is everybody's business, I make it a habit to consider who are the authors. If they are people who have no other profession than letters, I learn mainly their style and language; if they are doctors, I believe them most readily in what they tell us about the temperature of the air, the health and constitution of princes and and wounds and maladies; if they are lawyers, we must take what they say on controversies over rights, the laws, the establishment of governments, and things like that; if theologians, Church affairs, ecclesiastical censures, dispensations, and marriages; if courtiers, manners and ceremonies; if men of war, what belongs to their business, and principally the accounts of the great actions at which they were present in person; if ambassadors, negotiations, understandings, and diplomatic practices, and the way to conduct them." -Michel de Montaigne (The Complete Essays of Montaigne)