Interesting discussion. I'm a middle of pack triathlete trying to become a better runner. I just finished reading "running with Kenyans". I have to admit to loving my hrm and garmin a little too much. A couple of months ago, I managed to beat my (very slow) 5 year old 5k time by 3 seconds. I attributed this partly to using my garmin to pace myself to a pub. After reading the book, I decided to race another 5k ignoring my watch, and running on feel. I was pretty shocked to take almost a minute off my time. So I totally agree that having these numbers in your head can impose self limiting beliefs on a runner. I still use my garmin most days, but am far less a slave to numbers than I was.