While I've never had it happen to me personally, I have seen it happen to someone else. My wife and I were finishing up a ride at a remote trailhead on the C&O Canal Towpath when a pair of young women limped in walking their bikes. Both pedals had fallen off their shanks on one of the bikes within a few miles of each other. For some reason, the ball bearings fell out of their races on both pedals. One of the girls was limping with sore feet from pedaling on the bare shanks. Since my wife and I were finished riding for the day, I took the pedals off my bike, put them on the crippled bike and sent the grateful girls on their way. We were simply in the right place at the right time. We were staying in Cumberland MD. right next to the Cumberland Connections bike shop where I bought a new set. It gave me the opportunity to replace the marginal OEM pedals with a better quality pair. Not a common occurrence I'll admit but it does happen.