Easily the dumbest gun sale decision I ever made, was to trade the pre-64 Winchester 30-30 that my father bought me for Christmas in 1984, to a friend in exchange for some work I needed done. We estimated the value of the gun at the time to be $300. At that time, I had shot easily 200 pigs and a half dozen deer, including the first deer I took with a rifle, with that gun. My brother and I both got pre-64 Winchesters that year, and reveled in getting to know them.
Fast forward 15 years later and I still regretted that decision. I contacted that friend who told me he sold the gun to another mutual friend, and I was able to reach him. He wasn't interested in selling it back to me until I told him the story of how I got it. When I did that, he said "hell, there is no way I can keep it now - just get me a replacement and it's yours." So we were reunited after 15 years. I've now owned that gun for nearly half my life and plan to give it to my son someday, who is not a big gun guy, but when he reaches into my gun safe, he always comes out with that old Winchester.
I'm glad I had a second chance.
I've had other guns I probably shouldn't have sold, but that I can't say I regret selling. That Winchester though. I consider myself very lucky to have it back.