When I first discovered the underworld, I stayed away from it for a while. Soon though, I went down there a lot and collected lots of guide voodoo dolls, not knowing what to do with them. I also found a clothier voodoo doll, and figured that if I killed all of the NPCs, they would have a chance to drop their dolls too. Thus came my hours of literally burning through NPCs, killing myself at least 50 times in the process. Also, this was during my year long period of not knowing Hardmode was a thing. (Which is not as long as some people, but it frustrates me to this day.)
There was also the time in hardmode where my monkey brain somehow thought that the thing to summon Duke Fishron could only be found when its raining. Then somewhere I got the false information that rain occurs more often when you have big pools of water, and once I got the Bottomless Water Bucket, you can guess what happened. My world became atlantis for literally nothing.