I don't count anything I owned before I became an official knife knut, at about the age of 18. I seriously don't own anything I had from before that time.
Since then, I've lost 2 knives, and have had 1 stolen. I guess you could count the other 2 stolen, as I know where I dropped/left them, and they were not turned in, like they should have been.
Last time was about 5 years ago, and I'm not making those mistakes again. I ALWAYS check my pockets when leaving somewhere, and I never leave a knife loose in slacks. Jeans are okay.
Stolen: Buck 110, Alaskan Guide with S30V
Lost: Chris Reeve Mnandi in Ironwood, Spyderco Kopa Gold lip pearl
I've replaced the 110 and Kopa, but can't afford the Mnandi.
That's me. I always check my pockets before I leave. I try to be more aware of my knife if I ever have it out or if it's in my pocket. I used to carry my biggish type folders in my back pocket which I think contributed to my losing them. I also had a bad habit of setting my knife down after gutting a deer and completely forgetting that knife (till later). In that case, I learned to place the knife directly in front of me when setting it down so I see it instantly. Since then, I haven't lost a knife yet.