Scott Adams wonders why we are often accurate:
One theory is that we're good at predicting the quality of things from scant clues. But can you really tell if a movie will have a good plot, which presumably matters, from the first two minutes?
A second theory is that we make up our minds about things based on the first few irrational cues, and everything that follows is rationalization. So if there's something in the first two minutes of a movie that I like, for whatever subconscious reasons, I later think that the directing, acting, and plot were also good (enough), even if on some objective level they were not.
He believes in the latter.