What Are Some Things You Regret Buying or Bought but Never Used?

I would just say that not everything needs to be a BIFL product, but there can be a tendency to push towards recommending only buying the best of everything. Like, I cook a lot at home, so it made sense to buy a $200 chef's knife that I'll get tons of use from and decent sharpening stones to maintain the edge. I listen to a ton of music, so I've dropped probably around $1500 into a pretty good pair of headphones, a DAC and an amp. On the other hand, I solder like once every couple of years, so getting my cheapo $40 Amazon special made more sense than dropping $500 on a much better soldering iron that offers features I simply don't need and won't benefit from. Sometimes good enough is exactly that, but it can be a nuance lost in these discussions.

Heck, even though I use them several hours a day, my hearing just isn't that good for me to justify spending a substantial amount upgrading my current audio gear. Even if there is an improvement to be had, I'm not sure it would be something I could even notice, so I'm not tempted to go down the rabbit-hole of upgrading my DAC, amp or headphones, as it would be chasing diminishing returns that I'm not even sure would be perceptible for me at a simple biological level.