Well,
just take it. This is a already large and still growing community.
There may be thousands of reasons why someone would -- a post, anything
from bad content to rain outside may count here. The population of
this site must have reached a size where it is by far not a trivial
quest to understand it's dynamics.
The outcomes of voting are just one sign of this. If you find a way
to simulate this, you'll be quite a hero to me...