"I have spent time in the morning casting every part of the Fireball spell except the final trigger word four times, I need to rest and pre-cast it again."
Makes sense, in other magic systems, casters often have to recite the spell for a long ass time before casting. Would suck for DnD tho, imagine waiting 5 rounds of your friends taking a long ass time to do something basic while you stand there murmuring
That's the fluff of how the Vancian spellcasting worked for wizards in 3.5, and I keep it as my headcanon for 5th as well. It's not perfect, but is better than "whoops, forgot how to cast the spell even though I have my book of cheat sheets right in front of me!"
This is why I hoard scrolls. I may only have two casts of Fireball prepared but I have 13 more scrolls of it in my bag. I don't want cool magic staves or fancy robes or rings, I want to spend my loot on scrolls. My DM hates me because I like to keep a significant percentage of the wizard spell list just on hand in scroll form at any given time. Need flight? Here's enough for the whole party. Got petrified? I have a couple Stone to Flesh here. And of course all flavors and types of attack spell to dodge resistances.
The only problem is that at higher levels things start to resist reliably because scrolls don't use your actual caster level for checks and saves. Pathfinder has an answer to this in the Scroll Sage subclass but dnd players may have to resort to light homebrew.
2e does it the right way. Spells on scrolls are cast at the level of the wizard when writing the scroll. It's a nightmare to keep track of if the PCs start writing them but a great tool for balancing and story telling.
It works sort of this way in D&D too (and I suspect Pathfinder 1e since it's just D&D slightly modified).
The thing is the scroll's cost is based on its spell level x caster level. Usually you craft the scroll at minimum caster level for that spell, but they can be made up to the crafter's caster level. It just increases the price...a lot.
More importantly, the spell DC straight up just uses the casters at the time of casting. Fireballs will get pricy when you're keeping them heightened but they wont let you down by default
D&D sorta has that, too. Some spells can be cast as rituals, which take 10 minutes to cast, which is 100 rounds of combat.
The usual benefit of ritual spells is that they don't consume a spell slot, which fits very well with the idea that prepared spells require a similar amount of work that was just done in advance.