Pretty sure it fell out of my pack at a trailhead when I took my keys out of the pocket they shared in my pack. The pocket I very carefully never open during a hike because I don't want to lose anything in it. Damn my hands that swell so badly when I'm hiking!
I looked for it for a long time the next day, even used a metal detector. Found a lot of bullet casings. No ring. Someone must have picked it up, unless it rolled a distance off the road when it dropped. I put out an APB on Facebook. I could order a new one but I'd rather have the original back.