In 2007 Michael Mauboussin presented a big jar of jelly beans to his seventy-three Columbia Business School students. How many beans did they think it contained?

Guesses ranged from 250 to 4,100; the actual number was 1,116. The average error was 700 — a massive 62% — demonstrating that the students were awful estimators.

Now here comes the weird part. Even with all these wildly incorrect guesses, the average guess was 1,151 — just 3% off the mark. Not only that, only 2 of the 73 students guessed better than this group average.

So although individually everyone was woefully inaccurate, collectively the group was incredibly accurate.