Yes, this is a significant problem for most players in my experience. It’s generally very difficult to predict how many encounters you will have in any given day, and 5e is balanced such that the players are favored to win even if they don’t spend any limited resources. This leads to a situation where players are always saving such resources for a hypothetical encounter where they “might need it more” that never comes. I have had some success in persuading players that they should start thinking of every spell slot (or whatever) they still have when they take a long rest as a spell wasted. But, of course, the flip side is the 5 minute workday.
Just another problem 4e solved only for WotC to walk it back because it didn’t “feel like D&D” without it.
Yes, the sad fact is, despite the cries of protest being legion - 4e Daily, Encounter and at-will powers were excellent design. And not JUST for the reasons being discussed in this thread!
But to address the thread issue:
Assuming we table the time pressure discussion (it's been discussed ad nauseum in some recent threads), the problem really is that 5e PCs can waltz right over most encounters - right up until they can't.
Specifically - you have to throw A LOT of medium or less encounters, or even a decent amount of hard encounters to make a well functioning party sweat. So what to do you have to do if you want to make them sweat with only a few (or even 1) encounter? You have to go deadly.
And not the DMG version of deadly (which is defined, If I recall correctly, as the party being forced to spend 25% or more of its resources) but TRULY deadly +4 CR or much higher.
And the problem there (as I suspect @tetrasodium will affirm) is that it's still not TOO hard for the prarty right up until it shifts quickly (like falling off a cliff quickly) into TPK territory.
It takes an experienced DM to overclock the CRs well enough to challenge but avoid the TPK issue. Of course, one solution is to ensure the party can run from any given encounter (which, IMO, isn't as easy as it sounds - running in 5e, unless the party can teleport isn't all that easy).
But if you do that, we're right back at the 5/15 minute workday (again ignoring the discussion on time pressure, for the moment).
So yea, 5e makes it tricky.