That is what the money manager Guy Spier has spent much of the past 17 years trying to figure out. He believes that most investors pay attention to the wrong things and allow their minds to get hijacked by bad ideas.

So Mr. Spier has set about purifying the environment in which he makes investing decisions — changing his work space, altering the information he uses and, above all, continually trying to counteract his own irrationality. What he calls his “journey” is a transformation any individual investor should be able to emulate — perhaps even better, he says.

That journey accelerated in 2008, after Mr. Spier and his friend, fund manager Mohnish Pabrai, donated $650,100 to a charity and won a private lunch with Warren Buffett. After listening to Mr. Buffett, Mr. Spier says, he realized “I’ve got to hit the reset button and make drastic changes.”

Mr. Spier, 48 years old, is worth listening to. A graduate of Oxford University and Harvard Business School, he runs the Aquamarine Fund, a $180 million partnership specializing in cheap “value” stocks. Since its launch in September 1997, the fund has beaten the S&P 500 by an average of 4.9 percentage points annually, net of fees.

In a book to be published in September by Palgrave Macmillan, “The Education of a Value Investor,” Mr. Spier describes his struggle to improve his decision-making hygiene. (A disclosure: A friend and former editor of mine, William Green, collaborated on the book.)

Seldom has a successful money manager so painfully flagellated himself in public. In the book, Mr. Spier calls himself “blind,” “dumb,” “spectacularly foolish,” “misguided,” “stumbling,” “wrong,” “vulnerable” and, over and over again, “irrational.”