this article in Wired.
When students were simply asked to rate jams for flavour their scores closely matched those of jam experts. However, when a second group of students were asked to do the same task but to give detailed reasons for their decisions, they went haywire and rated one of the worst jams as the best.
Reason doesn't seem to be very good at helping us make decisions and might even get in the way. What it's very good at is helping us persuade others that our judgements are correct.
I don't know about you but I don't find this a very comfortable thought.