Sometimes you don't realize how much you like something until it's gone. Maybe you have a friend that trades you their game for yours or perhaps you just sold off a game at a store for a few $$. Either case, later on you may have regretted getting rid of them.
So what game(s) was/were that for you?
For me it's definitely be Mystical Ninja Starring Goemon for the N64. It's not the best game ever but it has a certain charm to it that I love. One day though a friend of mine offered to take it from me in exchange for 3 crappy games. I was 8 at the time and didn't realize I was screwing myself over in the deal. On top of that one of the games was for a system I didn't even own!.. Oh god, young me was an idiot. Well I never traded it back and I eventually moved away. Nearly 10 years later I found a copy of the game for $45 at a retro game store and I love it v.v XD
A runner up is Super Smash Bros. Melee and Pokemon Stadium 2. I'm not sure why I traded/sold these games -I did eventually get Melee back but I've yet to find a fairly priced Stadium 2 
