All the way back when I was taking the SATs, I remember being given the advice that, if in doubt about a question, I should go with my first choice. I never did, but finally there's an explanation for why I should have. If any other second-guessers are reading this - the explanation might help you before it's too late!
The oft-repeated wisdom is that everyone should trust their instincts. Fair enough. My instincts seem to dictate that I second-guess every possible decision, taking another look at what the right response is. Generally that second look involves my talking (internally) my way through the chain of reasoning that should get me to a conclusion. As it turns out, that's not a sound strategy.
Tim Wilson took a look at tests in which people had to take a position on an issue, and then evaluate it over time. If they had simply taken the position, their position stayed fairly steady over time. If they had had to explain the position, their position tended largely to change. Tim constructed his own experiments in which people either had to explain a position or simply take the position. Generally, these positions were political - asking subjects about their feelings about President Reagan, school bussing, or the death penalty. He then called the subjects much later for a phone interview, and asked them the same political questions, as well as a few control questions. Again, the people were far more consistent with their earlier positions if they hadn't had to explain them. The explainers much more frequently changed their mind.
But that was a complicated political position. What about a position that was instinctive and personal, without the need for real justification? Wilson set up a new test. He asked female students to come in and take a look at posters. They were then invited to choose one and take it home. (Only women were subjects because Wilson was concerned that sex difference might lead to a different choice when choosing posters.) Five posters were on display. Two were copies works by Monet and Van Gogh, and were extremely popular with general focus groups. Three were motivational posters, or funny cartoons. They were then given questionnaires. Some questionnaires asked the students to evaluate the posters. Some simply asked background information on the students themselves. Lastly, the students were invited to choose a poster.
The explainers generally chose the funny posters, while the non-explainers chose the arty ones. After a few weeks, when called back and asked about the poster, whether they would take it with them over summer, and how much it would take to buy the poster off them, the explainers were much less happy with their crappy posters than the others were with their nicer ones.
It seems that your brain is a rather lazy organ. If it can't find a reason why it likes something - and most people aren't able to easily explain why they like great art - it just decides to like the thing it can explain. "That poster is funny," "those politics are easy to justify," or "that answer sounds more right because blah," are explanations it can pounce on. It's only after time and reflection that we can return to our real instincts.