Hiya!
It's not that "every single fight, trap and hazard IS a life or death affair...", its that "every single fight, trap and hazard is a POTENTIAL life or death affair".
For example, lets say a 5th level PC with core stuff (no feats, no unusual race/class, no multiclass, etc) is in a forest. The PC has medicine for a sick town elder on the other side of this forest. This forest takes a day to go through, going around it takes 4 days. Thing is, the forest is known to be the stomping ground of a rather nasty Manticore. The Player decides to save time and head through the Manticore Woods as time is of the essence. Now, the DM can handle this two ways (at least).
Way Number One: The DM has the Manticore's stats...and it's bumped up a bit (near max HP's, missing an eye so -3 to hit with it's tail spikes, but it's old and bigger, so damage is +5 with the spikes; you know, a 'unique and tough' old veteran monster). The PC takes a wrong turn and ends up falling down a small cliff of 30' and takes 15 points of damage. Later that day, the PC just happens to have taken the 'easiest looking route'...looks like a large game trail. Of course this trail is frequently hunted by the Manticore, old Blackspike! The DM's notes say that once per hour of traveling 'in the open', gives a 1 in 12 chance that Blackspike find them.
Way Number Two: Same thing, but the DM pre-emptively decides "he won't encounter Blackspike, I'll just make it a black bear if Blackspike is rolled to show up".
Now, the problem is that with number 2, the DM has decided specifically to NOT go with consistency. This sets up the Player expectation that "The DM won't throw stuff at us that can kill us...at least not a 'random encounter'". HOWEVER, if we look at number 1, and the DM rolls a Blackspike encounter, and keeps it as rolled...and the PC dies. Well, that sets up the Player expectation that "The DM isn't going to save me...that's on me".
So the potential to meet up with a deadly foe was completely up to the Player. He could/should have known "If I go through the woods, alone, Blackspike will kill me if I encounter him. No way can I fight him alone. Hmmm.... Nope. Not worth the risk. I'll take the long way" ...OR... the player can decide "If I go through the woods, along, Blackspike will kill me if I encounter him. No way can I fight him alone. Hmmmm... I'll have to risk it. The elder doesn't have the time". In the Players mind... HE has made the decision and has to live with the consequences.
This ties into the BBEG expectations. In a campaign with death being a possibility "at any moment" (re: the DM isn't going to 'lessen' encounters or build them specifically towards the PC's strengths/weaknesses), when it comes time for a BBEG, the expectation is "This is the climactic battle! It's very likely that some of us die...hopefully we win and save the Princess". This is a far superior (IMNSHO) situation to have than "Oh, it's the BBEG. It's gonna be tough...be we'll probably win...and those of us that die will probably get Raised somehow after".
In the former case...a 6 round combat with the BBEG is NOT a problem...it's a goal!
^_^
Paul L. Ming