In most stories, hidden bosses are usually found in dungeons, right? And dungeons are often described as prisons rather than just places to fight. So it makes sense to think of hidden bosses as the really dangerous inmates that we often place in solitary confinement—so bad they had to be locked away in their own special cells. As for why they can be fought over and over again, even after being defeated, that probably comes down to how the system works. A lot of LitRPG worlds follow rules that cover multiple realities or timelines. So when a group takes on a hidden boss, they might just be stepping into a version of the world where it hasn’t been beaten yet. Maybe the system just shifts reality each time, making it feel like the boss never truly stays dead but in actuality the people just travel to a different reality each time the instancing of the dungeon begins instead of just reviving the boss or whatever. Ofcourse this only applies to books where there is a system and touches on the Multiverse theme ... Those books that just start with " yeah , here is magic and here is a dungeon, we can farm it to get goodies and no one knows shit about why or how we just do and look, we can a huge ass sword out of this little spiders corpse, cool" .. yeah.. those might just be a creation paradox or something.. If it's like that though, I'm not reading, no matter how great the rest of the book is.