A Brief Explanation of the “Wisdom of Crowds”

Let's compare the median estimate of a crowd with the estimates of individuals. If the median estimate is an underestimate, half of all individuals will be less than the median estimate and thus further away from the truth. There will also usually be some individual estimates above the median that are also further away from the truth than the median. In other words, most individuals will be further away from the truth than the median estimate and similar reasoning applies to overestimates.

On the other hand, a crowd of people who are adjusting their beliefs to follow the crowd will be less accurate than a crowd of people who aren't adjusting their beliefs. The consensus is more accurate only when we don't talk about it.