From Seth Klarman, via Margin of Safety:
How Much Research and Analysis Are Sufficient?
Some investors insist on trying to obtain perfect knowledge about their impending investments, researching companies until they think they know everything there is to know about them. They study the industry and the competition, contact former employees, industry consultants, and analysts, and become personally acquainted with top management. They analyze financial statements for the past decade and stock price trends for even longer. This diligence is admirable, but it has two shortcomings. First, no matter how much research is performed, some information always remains elusive; investors have to learn to live with less than complete information. Second, even if an investor could know all the facts about an investment, he or she would not necessarily profit. This is not to say that fundamental analysis is not useful. It certainly is. But information generally follows the well-known 80/20 rule: the first 80% of the available information is gathered in the first 20% of the time spent. The value of in-depth fundamental analysis is subject to diminishing marginal returns.
Most investors strive fruitlessly for certainty and precision, avoiding situations in which information is difficult to obtain. Yet high uncertainty is frequently accompanied by low prices. By the time the uncertainty is resolved, prices are likely to have risen. Investors frequently benefit from making investment decisions with less than perfect knowledge and are well rewarded for bearing the risk of uncertainty. The time other investors spend delving into the last unanswered detail may cost them the chance to buy in at prices so low that they offer a margin of safety despite the incomplete information.