Many years ago, I was riding home one night and hearing the distinctive sound of plastic on tarmac, I presumed I'd ridden over something made out of plastic. Got home to discover that that sound was my back light falling off... dang!
Some weeks later, a friend was telling me about his great little back light; it's bright and batteries last for ages, and best of all, it cost him nothing as he'd found it on Greyhound Bridge. "Where abouts?" I asked. "...near the end just before the bus stop??" I added. Yep, he'd found my back light.
(I did let him keep it)