Anyone who actually runs a RPG knows one thing for absolute certain - there is no time to consider your DM style or "how you DM" while you're DMing. You simply DM how you DM, thinking about how you DM is a between-sessions thing, or your game is incredibly boring and your table is credibly empty. And thinking about how you DM between sessions will not necessarily change how you DM. It's an overly pointless endeavor, really.
There are hundreds of idiot content creators on YouTube who believe otherwise. They think that thinking about it hard will change what happens during the game itself and it will, but only for the worse. Because 'good right now' is universally better than 'better in a minute'. Because time is the most valuable commodity at the table. Any prep that shortens downtime or 'dead air' immediately increases the quality of play. There is no getting around this. Any resource that pretends it's for use at the table is wrong. At the table if an adventure module is used it should be the only thing used.
The corebook shouldn't be. Generally the core should be held by the player with spells if you don't happen to have spell cards that explain the entirety of the spell's description. As an aside: if you have spell cards that don't explain the entirety of the spell's description, you should throw them away, because they are garbage. Get the correct spell cards for the job.
As a DM you should have the rules memorized. Those you haven't memorized should likely be charts printed on a screen for reference. If it can't be memorized or put on a screen, you're running the wrong game. Or you haven't invested into it properly to be able to effectively run it yet. I keep Hackmaster 5E on my shelf as a reminder of the kind of dedication it should take to master a ruleset and memorize every element of it to the point it is intrinsic. Some people have a better tolerance for rules ingestion than others. I envy those who can competently GM Hackmaster 5E. It'll never be me.
But there is a stark difference between Hackmaster and something insane like ACKS. Hackmaster realizes and details things important to the game. ACKS was written by a lawyer who would much love to spend his free time pretending to be an accountant. There is a difference between necessary-but-boring design and minutiae design for the sake of minutiae. ACKS is in the later camp. And that was before it's current expanded edition I haven't bothered to read and I presume nobody has ever bothered to play. My guess is everyone who pretends to play ACKS actually plays B/X and pretends otherwise. And my guesses have a tendency of being better than other people actually knowing things.
Back to the point: You shouldn't be thinking about rules during play, you should *know* them. You shouldn't be thinking about how something will play out, you should just *react*. Your gut will get you there. The system will provide. If it doesn't, you're playing the wrong game
Also, content creators don't realize this because none of them are really being honest with their audience or perhaps being honest with themselves.
