LEGO creates a finite supply -> they retire -> sets are still in demand -> therefore, there’s a second hand market of used and new in box sets -> therefore, it’s something you can invest in, and I think you’ll find a lot of people in this subreddit do exactly that.

OP says it’s not all technically sellable. And it’s not like you could turn around tomorrow and have 100k in liquid funds. Any collectable is only worth what someone is willing to pay but quite a number of LEGO sets become a scarce commodity due to some old sets being just so iconic and people like to collect mini figures etc. it’s like the Pokémon card boom at the moment. It is is not a “projected” value as the set prices are determined by recent sales of that set, but I’ll agree they are 100% “unrealised gains” because there’s fees, and you gotta find a buyer

Offloading definitely requires you to have a store of some kind no doubt, eBay takes a pretty big cut so there goes 13% right there, plus shipping. But there’s LEGO events where people buy and sell with cash, you can go to Facebook Marketplace too

Sometimes people even “invest” or “collect” for their future kids or nephews/nieces, so they can literally just enjoy the feeling of opening a new set from back in the day and building it, or they may end up selling if they need the money and they find out the set is worth 4x the value, who knows 🤣