The problem being that we often find ourselves doing things for reasons other than the ones we think we do. Robin Hanson will tell you that.
Why is this a problem? (Along the lines of, why do you need to accurately know the reasons why you do things?) I'm trying to relate. I see beliefs as something I need in order to decide what to do. As long as I'm doing what I decide to do, why would I worry about varied reasons for doing it?
It has been claimed on this site that the fundamental question of rationality is "What do you believe, and why do you believe it?".
A good question it is, but I claim there is another of equal importance. I ask you, Less Wrong...
What are you doing?
And why are you doing it?