Introvert Edit: After seeing everyone else's responses, I feel obligated to expound a little on my own answer: I'm an introvert, and I think that this is directly caused by my stutter. Being extroverted comes naturally, but it's like trying to shoot a gun that jams on 70% of the bullets. It can be more than a little embarrassing at times, so I prefer to just keep my thoughts mostly to myself. This has had its benefits and disadvantages, but I'm happy with my choice.