Uhhhh
Uhhhh
Uhhhh
Let me check my spell list. Huh. Okay, now I need to check the source book, oh wait, it's in this expansion...
If only players could either memories their spells or assemble a cheat sheet/cue cards for those. That's what phones could be useful for...
Player tip: either use the Spell 5e app or Emmet Bryne's custom class sheets. Or both, like I do.
I used to print out spell sheets and put them into some sort of a spell booklet for reasons like this. It also helps that I played a bard when I did that and so there wasn't a whole lot of spells that I needed to keep track of.
The last time I played a wizard, I just relied on a similar tactic (one-spell sheets compiled into some sort of a booklet), but instead of printing it out, they just stayed as files that I move to a directory on my phone called "prepared spells".
I had a pretty disastrous fight with my wizard, so I came up with a little list of "when X happens, use A,B, or C". That made combat much easier, since it had a list of escape methods for when I was cornered, spells to deal with invisible monsters, stuff to deal damage when I was in a safe spot, etc.
It only had five or six entries, but it made my turns way faster in combat.
If this happens, the RPG is too complex for that player. Play a simpler system.
I almost exclusively run PBTA games nowadays because of this. And if the players are totally inexperienced we'll run a one-pager like Lasers and Feelings or Honey Heist first.
Rules just bog down the play speed too much unless everyone is an expert, paying attention, AND not drunk, which is basically never.
This js why if i play casters in dnd it's a sorcerer. Much smaller list of spells known so it's easy to know wtf im gonna do