I was out mountain biking yesterday, and due to some wet trails, I was on the ground a couple of times, even got a nice gash below my knee from hitting a rock. One of the other riders that was also on the ground a few times said "if you aren't falling, you aren't pushing yourself enough."
I came across a similar quote in Tribes. The quote was "If we're not uncomfortable, we aren't doing enough leading." It's that whole comfort zone thing again. We have to get our of our comfort zone to be effective, as leaders or bikers.
After my second painful fall yesterday, I did back off and become conservative in my riding for the next hour. After that, I got past my fear of falling and was pushing again, and having much more fun. Just like in life, it was only my fear that was holding me back, not my ability.