I agree it's pretty hard, I catch myself getting scared sometimes and substituting words. I think the reasoning behind it is to reduce anxiety and to not let your stutter hold you back. I remember reading a story about a relatively successful person with a somewhat severe stutter giving a presentation to her executives. The executives all said afterwards that they were impressed with her, that she didn't let her stutter hold her back. That's where I'm trying to get to. Imagine how free your personality would feel if you weren't nervous about speaking, ever.