Don't feel bad. I lost a U-Lock.

I stopped at a grocers to pick up some iced tea and a loaf of bread. I put the shopping bags into a handy grocery cart, unlocked the bike, put the lock into the grocery cart, unfolded a basket, put the groceries into the basket and rode off - leaving the lock in the grocery cart.

I went back the next day. No one had turned in a lock.

It was the most expensive iced tea and bread I have ever purchased.