Just to get it out of the way, I don't watch CR, so I don't know if this is a specific reference, and am just speaking about D&D in general. :)

Kind of inevitable with most D&D games. If you design adventures around having a series of more-or-less balanced encounters, almost always combat, where player characters are expected to be stressed but not generally killed the vast majority of the time... both the players and their characters are going to have the expectation that they can just do that.

So you need to manage those expectations. Make it clear up front, and either run the game so that death is a real threat more of the time, or find other ways to make it crystal clear when it is.

(Or just don't make things lethal and find other consequences for failure. Or whatever you'd like, my point is just to get folks on the same page.)