In 1999 winter commuting I went down on black ice. Hit real hard, had no time to react. Bruised the hip and knee, but the bike seemed ok. 15 years later I am accelerating up a hill on the way home from work and "Snap"! left crank arm breaks off about 40mm from the pedal. Looking at the break it was very corroded about half way through. Happened to be same side I went down on that one winter 15 years before. I know it was a crack from that fall that had been eating its way through the crank arm for a lot of years and miles that caused it to fail. Rode home one legged.