The fear in and of itself can make you fall! The first time I went out clipless, I fell in a creek that ran alongside the trail. I had been clipping/unclipping for 25 miles. We stopped for a quick rest and I left one foot clipped in, but didn't brake, leaned and took off and rolled down a bank of rocks and into the creek. No less than 10 riders standing there watching me make a you-know-what out of myself.
After that, I took the clips off and rode on platform pedals for about 3 months. Then I did the double-sided pedals for about 2 months. Then went to Speedplays... I've fallen a few times with my Speedplays, but always when I'm not focused and always when I don't have complete control of the bike.
So, it's important to be able to relax and focus... if you are all bunched up with fear, falling will become a self-fulfilling prophecy.
Remember, we ride for FUN, right?
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"I never made "Who's Who"- but sure as hell I made "What's That??..."