James Surowiecki's 2004 book, The Wisdom of Crowds, suggested that the more minds you have working on a problem, the better the solution they produce. For example, if a large number of people were asked to guess the distance between Salinas, California and Geneva, New York, averaging their responses would yield a result closer to the actual distance than any of their individual estimates.
Now, a couple of researchers from MIT and UC San Diego have found that, when people are asked to estimate an unknown value a second time, the average of their two guesses is more accurate than their first guess. Psychologists had assumed that, when individuals are asked to estimate an unknown value, they would make their most accurate guess first. To have them guess again, it was assumed, would yield a less accurate guess. And thus, if you averaged the two guesses, the average would be less accurate than the first guess.
Vul and Pasher recruited 428 participants and asked them eight questions from the World Factbook (i.e. "What percentage of the world's airports are in the United States?"). Half the participants were then asked to make a second guess immediately after the first. The other half were asked to make a second guess three weeks later. For both groups, the average of the two estimates was more accurate than either of the estimates alone. Those who were asked for a second guess immediately after the first improved their accuracy by 6.5%. Those asked for a second guess three weeks later improved by 16% (perhaps this second improvement is due to ensuing Google-fever?).
In my book, The Breakthrough Company, I found that companies that developed strategy iteratively -- returning each quarter to key questions about the company's position and path -- adapted more quickly and typically outperformed their competitors. Here's more evidence that second-guessing yourself isn't such a bad thing after all.