I've probably forgotten half the knives I've lost over the years.
First one was the 3-blade Old Timer my father gave me for Christmas when I was 5 years old. I was whittling sticks on the back porch, when mom called me in for dinner. I forgot it on the back porch. Thought I'd lost it forever. 25 years later, when my father passed, I found it tucked away in the bottom of his gun cabinet. No idea why he never gave it back.
I've lost not one, but two Kershaw Leeks. One I lost doing forestry work in the swamps around Camp Lejeune. Caught on some brush, and pulled out of my pocket. I searched for it for an hour, but it was in thick swamp, under calf-deep water. Never did turn up. Perhaps during a dry season, a young marine on a training mission found himself a new pocket knife.
Lost another one doing the same kind of work in the Hoffman Forest. And a small Buck folder near the Dare Bomb Range in Dare County.
Somewhere up in Caswell County I lost a Leatherman Wave. My favorite multi tool. I've got a few others, but none of them fit the bill quite like it did. I still don't know why I haven't picked up a new one.
Lost a slim Kershaw folder while in Dare County. I assumed it was gone forever, but a few years later, when I was assigned a new work truck I found it. I had to take the seat out of the truck to remove some of the radio gear, and there it was, lodged underneath the radio amp. I don't carry that knife to work anymore. But its my daily carry when I'm out and about.
Thought I'd lost another Buck folder, while replacing the axle in my 03 Mustang GT. Found it a year later when I'd took out the spare tire. Somehow it got under it.
And I'm sure there are many others that I haven't lost, only put away, and then forgot where they ended up.