[geekingfrog]

This effect comes from the effect of regression to the mean. Some people will vastly overestimate, while some people will vatsly underestimate, thus cancelling out.

It holds as long as the people used are very diverse (not under the same cognitive bias) http://www.socialresearchmethods.net/kb/regrmean.php

[dthunt]

If you ask people to estimate the number of protons inside the sun, you might develop a peak around some sorts of numbers, but it's not likely to be a particularly good estimate.

[gravity13]

Well, yeah, we all have a cognitive bias in that we've never had to comprehend a scale at 10^35-10^45 before (that's my belief graph btw).