I "lost" mine a few years back after climbing Whitney. It's far too long of a story to recreate here but suffice it to say, I had just hiked 22 miles, beginning at midnight the night before and once I got back to the Jeep I needed to cut a replacement 'window' out of cardboard (bear in mind, I was whooped at this point and just wanted to crawl into a sleeping bag and get some rest). I went to a small market in Lone Pine and rummaged through their dumpster to find some cardboard big enough for a replacement front passenger side window.
Once I got to cutting the window, with my knife, an older somewhat friendly guy approached and talked to me as I was fashioning a new window for my drive back to CO. By the time I was in the duct tape stage of the process, he told me to have a good evening and walked off.
After I taped on the new window covering I went to the back of the vehicle to get my knife off the bumper. It apparently was too much temptation for the talkative stranger as my knife was now gone from right where I'd set it.
Thankfully I'm a big fan of spares so I pulled it's identical twin out of the safe when I got home, but having something stolen leaves a bad taste...