Some people treat game mechanics as the in-game physics of the world the characters are in. One knows specifically how powerful they are (their level) and how many times they can take discrete actions each day (spell slots), including exchanging other discrete actions they have for ones they don't (using a 3rd level spell slot to cast a 2nd level spell frex), and exactly how much a certain amount of rest time is required of them to regain a discrete action they no longer have (Arcane Recovery). So the Wizard in-world can calculate all of that and know precisely how much they can do each and every day.
But other people translate the game mechanics into a narrative conceit. For instance, narratively translate spell slots into a pool of magical energy they can tap into to create magical effects (and I say 'narratively' because they are suggesting the in-world idea is magical endurance, and not the actual change of game mechanics to using Spell Points). For those players, the character might be able to cast a certain spell a whole bunch of times per day based on need (using their 2nd level spell slots and/or 3rd level, 4th level, Arcane Recovery etc.) but how and why there ends up being a limit is never worried about "in-world". At a certain point in a Wizard's career they might cast Scorching Ray just once on one day, but then 10 times the next. And how and why that occurs within the world is just due to what the narrative ended up being-- not that it's because the game mechanic dictated that this was the only amount the character had the capability to do.
Neither way is the right way to look at it, and neither way is the wrong way to look at it. It just depends on how one makes the connection (if any) between mechanics and in-world effect. Me personally? I handwave so many hundreds of "mechanics as physics" issues throughout the course of a single game session-- where game mechanics make literally no sense to me as any sort of representation of "real life" in the game world... that I just give all mechanics a narrative washing over. I've stopped worrying about it. Why does the Wizard only cast Wish once per "long rest"? Because that's just what happened in the story that day, not because the physics of the world wouldn't let them cast it a second time. That's what works for me and is what I do. If others look at it a different way... that's cool. No skin off my nose.
But other people translate the game mechanics into a narrative conceit. For instance, narratively translate spell slots into a pool of magical energy they can tap into to create magical effects (and I say 'narratively' because they are suggesting the in-world idea is magical endurance, and not the actual change of game mechanics to using Spell Points). For those players, the character might be able to cast a certain spell a whole bunch of times per day based on need (using their 2nd level spell slots and/or 3rd level, 4th level, Arcane Recovery etc.) but how and why there ends up being a limit is never worried about "in-world". At a certain point in a Wizard's career they might cast Scorching Ray just once on one day, but then 10 times the next. And how and why that occurs within the world is just due to what the narrative ended up being-- not that it's because the game mechanic dictated that this was the only amount the character had the capability to do.
Neither way is the right way to look at it, and neither way is the wrong way to look at it. It just depends on how one makes the connection (if any) between mechanics and in-world effect. Me personally? I handwave so many hundreds of "mechanics as physics" issues throughout the course of a single game session-- where game mechanics make literally no sense to me as any sort of representation of "real life" in the game world... that I just give all mechanics a narrative washing over. I've stopped worrying about it. Why does the Wizard only cast Wish once per "long rest"? Because that's just what happened in the story that day, not because the physics of the world wouldn't let them cast it a second time. That's what works for me and is what I do. If others look at it a different way... that's cool. No skin off my nose.
