I have. I was young and didn't know any better. I think i've sold or traded off five or six, not exactly sure... but most all of them I really wish I had back, although I can't explain why, other than I don't have them anymore.
I had a running buddy growing up that could sell ice to a penguin. He'd start out with $50 in an RG .38 Special, and three trades later he'd have a 686. I thought, "Man, I could do that too!" After a few tries, losing my shirt in the process, I decided I'm not much of a trader. I'd see something I like and think I had to have it, no matter what. I had to give up that practice.
Since then I've pretty much decided to figure out what I want, then buy it and plan on keeping it forever. That being said, I do have a few guns on hand that I like a lot less than some of the others... and I wouldn't be surprised if I were to let them go at some point, but I just haven't yet because of "the rule"...