Observation One: There are two sorts of fights in an RPG: Fights that are supposed to be easy and fights that are supposed to provide a challenge.
In other words, first, there are fights that will almost never ever kill a player, also known as trash, or trash mobs. If your trash mobs are frequently killing the character, your balance is messed up. (Early versions of Avernum 6 had a big problem with this.) Most of the time, the vast majority of the fights in a game will be this sort.
Then there are fights that the player can possibly lose (mini bosses, bosses). And, of course, for fights that can kill the player, there is a spectrum of how likely that end result is. Some bosses will only kill you if you really aren't paying attention. Others require actual skill and strategy, and maybe a few tries to get your tactics down.