I sold more than 75% at one point. I kept only a cube, an assortment of commanders, cards that paired well with cards from the cube and the commanders to make commander decks, and one legacy deck. My collection went from a dozen boxes and 2 binders with over 2k cards each, to a single holiday box (the ones they used to make with 3 rows). It was a huge upgrade in how I related to the game. I try very hard to keep my total collection to less than 2500 cards now. I don't keep draft chaff (I give it away to newer players). I don't crack packs (I just buy singles). Every few months I do a "does this spark joy" through my entire collection, and trade away whatever I can. My goal with each card is to find a reason to get rid of it (with the exception of anything currently in a deck or top loader, which are obvious reasons to keep). It still creeps towards 2500 cards with a wishlist of about 1000 more, but it's quite enjoyable to feel like I concentrate the quality of the collection instead of just keeping "whatever".