I have never sold or traded, and then regretted it. So, all that have “gotten away,” and caused pain or anxiety, were lost. These have been Spyderco knives, clipped into a pocket. The one that hurt most, was losing my Spyderco Mariner, in the Eighties. This occurred in the Trinity River delta area, in SE Texas, during a kayak or canoe outing, so, there was no floor, upon which to hear it impact.
I have learned to consider any pocketed, clipped-in knife, to be an expendable, consumable item. If anywhere near water, a lanyard, or dummy cord, is a best practice. I have removed the clips, from some of my Spyderco and other knives.