The issue is that these limits are a well known part of the fiction. A caster knows in-game they can only get off so many spells of a particular level. Unlike in the real world where an athlete may try to push on, a barbarian knows for a fact that that can only rage twice before sleeping. It is a hard and fast, observably, repeatable fact.
So the problem is thaqt you are wrongly trying apply the real world as the physics and logic of the world. Just like a high level barbarian knows he can take multiple chops in the stomache with a great axe without falling or being impared, they also know they can only rage four times - this is their reality. Trying to map our reality onto it, where a "daily power" isn't part of our physical world, is just as wrong as saying no spells work. In their world spells work, you can rage a set number times per day, and water is wet.
I get it but it makes me shudder.
"Hey we need to hire a mercenary when we assault the fortress"
I will never say, in character,
"Let's try to hire a
Barbarian because we need to someone
who can soak damage"
soaking damage isn't a 'thing' in my fiction. And neither are barbarians - unless there is a group called barbarians by another group who considers themselves as 'more civilized'. As a DM, I try to separate meta terms from the narrative. "We need to find someone who is 'experienced and has a reputation of being 'tough as nails'. I never feel the need to tell the players what class they are hiring. If they're looking for a spellcaster, it might be easier to guess that the guy with the book might be a wizard.
That said, I get that that people have 'limited reserves' and that they need breaks and, overall, people know their limits but, on the other hand, I feel there should be some in-game knowledge before a character says, "yeah, maybe going in there will be too dangerous." Otherwise, it's just me thinking, "I need another level". My character has no idea what 'levels' are and if the fiction doesn't inform my character's decisions, then there's no reason to delay an action based on 'what level am I'.
In the end, I asked my DM to refrain from commenting, out of character, about the adventure itself. The little comments like, "oh, I didn't think you'd get here so soon!" or "I changed this part of the module".
I just don't need to hear it. I'd rather in-game foreshadowing. I think that may be part of what was influencing me. I don't mind discussing this stuff, after the fact, as a debrief of the game, though. Taking rests can be jarring as well as well but it's way easier to justify a character's limits. And, overall, I think I may just be overthinking it. I think I was Trying to predict the flow of the game on the meta-level. Which is a stupid thing to do. I just need to play the game.
Edit: just to clarify: this wasn't a DM problem but I did ask him to help me with my personal issue regarding the topic.