Nobody has any idea of what it implies except "really, really big", so when your concepts get up there, people have to do the math, since the numbers mean nothing.

This applies just as much to numbers such as million and billion, which people mixes up regularly; the problem though is that people dont do the math, despite not understanding the magnitudes if the numbers, and those numbers of people are actually around.

Personaly, if I first try to visualize a crowd of a hundred people, and then a crowd of a thousand, the second crowd seems about three times as large. If I start with a thousand, and then try a hundred, this time around the hundred people crowd seems a lot bigger than it did last time. And the bigger numbers I try with, the worse it gets, and there is a long way to go to get to 7'000'000'000(# of people of earth). All sorts of biases seems to be at work here, anchoring among them. Result: Shut up and multiply!

[Edit: Spelling]