Opinions are mostly made up on the fly:
For example, in two surveys spaced a few months apart, the same subjects were asked about their views on government spending. Amazingly, 55% of the subjects reported different answers. Such low correlations at high frequencies are quite representative.
And here’s Robin Hanson:
If you talk a lot, you probably end up expressing many opinions on many topics. But much, perhaps most, of that you just make up on the fly.
BS is something the BSer thinks will sound plausible. It lacks thought behind it because thinking is hard work. A BSer isn’t trying to be a Truth-Seeker, he’s trying to signal intelligence.
What’s interesting about BS is that people have different abilities to detect it, you might call them greater or lesser bull-takers. The grand hope of a bullshitter, of course, is he’s found himself chatting with a bull-taker who will just take it.
Bullshitting (as a phenomenon) is relatively easy to figure out, I think.
But what’s the theory of bull-takers? Why is listening so hard?
Not Unreasonable 
Instead of “why is listening so hard,” shouldn’t the question be “why does it seem so socially inappropriate to call bull-shit?” I vote for a social reform where the bull-takers stand up and put an end to the rambling commentary coming out of people’s mouths.