When I was in high school, my Dad was still in, "Take things away if he doesn't behave" mode. Sometime in my Freshman year he took all of my gaming materials, comic books, etc. and locked them in a trunk in the garage. Most of this was TSR stuff AD&D, Gamma World, Star Frontiers plus a few other things like Traveller. As I progressed through high school, I shaped up and found other games, so I mostly forgot about the trunk. After I graduated, my Dad asked me if I still wanted the "D&D stuff" in the trunk. Thinking I didn't particularly want the D&D books, I said not really. So he sold the entire trunk to somebody at work, which was not what I wanted.
Then about 10 years ago I willingly sold off the vast majority of my gaming material - books that I never used or did not want. This included tons of GURPS, Rifts, other Palladium games, the entirety of my Cyberpunk collection, HERO, and quite a number of others that I had accumulated over the decade before that. The only things I kept were games that either I could not bring myself to part with (both copies of TFOS and my Mekton books), games I was actually playing (Tribe 8, Jovian Chronicles) or games that I really enjoyed (Blue Planet). I've never regretted it and to this day the only things I've really added to my gaming collection are Exalted books, and a few books for games like Blue Planet or Jovian Chronicles that I was missing. I did buy several D&D 3e books when it first came out, but as soon as the nostalgia wore off and I realized I wasn't going to get to play I sold them to a friend of mine.