If your characters know that if they do A and B they will get C, then C can be the revelation that they are in very deep trouble (this, BTW, is the archetypal CoC adventure).
So, the more they breezed through A and B, the more they conserved resources (spells, potions, ammo, sanity...) to deal with C.
Then there is what I call "a narrative trope". The best example is when I, willingly, as the DM, throw everything at them, forcing them to never act but always react, with growing desperation (watch the last third of "Aliens" for an example). If done well, this will leave the players exhausted, maybe in a dire general condition, but happy - because the whole point was to survive.
(As a general rule, while DMing I hate the "Intro, progress, time for a battle, progress, time for a battle, more progress and so on" structure. That's for videogames, not for a game where a, hopefully, intelligent mind can weave an interesting plot structure. Battles, IMHO, should almost always be set-pieces tied to narrative plot points, and their nature should represent the meaning of that plot point - with the random wandering monster encounter sometimes thrown in for flavour).