It's one of those circular mind %&^$ where you believe that everything you believe in is what the majority of everyone believes in, because everyone that you associate with believes what you believe in, but what you fail to realize is that everyone who associates with you does so because they agree with everything that you believe in, so since your world is narrowed down to everyone that believes in exactly what you believe in, you think that the world (or at least the majority of the world) believes in what you believe in.
That is harder to sustain, if you have a job, work with the public, talk to neighbors, have outside interests like exercise, etc.
Conversely if you draw ever inward, shelter yourself, you can conclude that all your contacts think as you do.
We once had a very prolific poster here that guaranteed McCain would lose his primary to Hayworth, since everybody she knew was voting for Hayworth.