This could be something that you bought for a higher price than what most people would guess based on the item, or it could be something you bought for a normal price that has gained significant value as time has gone on.
What made me think of this question is a LEGO minifigure I got with my “The Hobbit: An Unexpected Journey” disc. It is Bilbo Baggins in a blue coat that was apparently only sold in that movie box only at Target stores. Even considering the exclusivity, I would have guessed maybe $10-20 for such a tiny piece of plastic, but there are sold listings on eBay from $80 to $225. I could possibly even get towards the higher end of that number since I still have everything in the original box in good condition. It’s not worth a ton compared to some other items people may own, but I think most people would not expect nearly that amount.
I’m not cool like everyone else here who got bargains or things that went up in value but for things that are more expensive than they seem to rational people, I have $6k headphones and up to $9k pens. Got them for a little under msrp (for the headphones, the cost of the pens went up).
Rational people don’t generally expect the prices of things like that to get so high, but they actually get a lot higher, I’m also not cool like the people who have those. There’s likely other things like this I can’t think of rn, but pens and headphones easily get the biggest “what’s wrong with you?” probably because they’re handheld non-jewelry