For many people, there was a singular gateway into the tabletop roleplaying hobby. Regardless of whether you started tabletop roleplaying games after playing a solo game book, a cRPG, as a graduation from board games, after watching live plays, or by being inducted into somebody's gaming group, it all actually starts as a frame of mind. You're a gamer, a problem solver, a geek. You correlate seemingly unrelated outputs, you reverse engineer how those effects have been produced, and then you design a series of input to alter or reproduce the same results. This is true whether you're playing a board game with a specific win condition, or a roleplaying game with a set of desired states, a wargame with optimal strategies, or just a friendly debate over whether Godzilla or Voltron would win in a fight. The process of gaming strongly relies upon analysis, over-analysis, research, debate, testing, and reflection. Which is why I get very confused when I see people online insist that it's bad form to "stop" a game to refer to the rulebook. On the contrary, referring to the rulebook is an integral part of playing a tabletop game, for lots of reasons, including that it's a lot of fun.
Part of the fun of a tabletop roleplaying game is building a simulation of an alternate reality. Forces in the simulation have different effects than in the real world. You can get hit with a club and set on fire and fall 100 feet and not die because your hit points said so. You can step through a portal to another world. You can create pocket dimensions because you memorised a magical spell this morning.
These pretend events may be fantastic, but they're also predictable. When you send a magical fireball into a room, it creates a temporary state of 8d6 damage. Within that state, creatures may manage to save themselves against taking all of that damage, but that in itself is also predictable. You don't cast Fireball and wait for a force beyond your control to decide how much potential damage you've created. You don't get hit with a Fireball and wait for a force beyond your control to decide whether you can attempt to dodge out of the way to take half damage.
It's all written into the rules.
For many players, experiencing the simulation is a considerable part of the fun of a roleplaying game. The effects of a simulated alternate reality are fun to witness, and even more fun to stress test. What happens if I throw a rope through a portal? Does the end of the rope stay behind when I pull the rope back? What happens if I tie one of the beads from a Necklace of Fireballs to the end of the rope and throw that through the portal?
We've all had debates over how fantasy physics functions, we've all remembered rules incorrectly and played them wrong for the better part of a year, we've all discovered new rules hiding in a caveat of a footnote. Rules provide structure and definition to the simulated realities we play in. When you refuse to look up a rule, you're accepting willful ignorance. The answer's there, but you're choosing not to look at it. Sometimes that's useful, because there is a rhythm to gameplay and it's not always appropriate to interrupt the flow of a scenario to refer to technical documentation. But it's also not always appropriate to not refer to technical documentation. Sometimes, it's actually more fun to look it up, because the answers to what seems like an idle question can often genuinely surprise you.
Some of my best gaming memories are the seemingly idle "rabbit hole" conversations my groups have had about how our game world functions. As geeks, we invariably wanted our arguments to be well supported by existing law. We didn't want to assert that 2+2 was 4 if there was a rule clearly defining the sum as 5. So we referred to the rulebooks. We read the letter of the law, and pondered the original intent and context. These conversations didn't always lead to anything of consequence, but they almost always effected how players interacted with, and the game master built, the world.
If you don't look up a rule, you'll never learn the rule. Through repetition, you begin to remember the rules of your game, and after a few game sessions you've committed to memory 80% of what you need to play. The remaining 20% can be looked up as needed or, even I admit, deferred for later reference. But if you also want to commit the remaining 20% to memory, then you do need to look it up, and when you look it up together as a gaming group you all benefit from the educational moment.
If we wanted absolute rules consistency, we'd play a cRPG video game instead. There'd be no contextual interpretation of rules, there'd be no flexibility, no exceptions, no arguments about whether the intent of a rule matches the written word. We don't do that. We play tabletop games, in part, because humans are adaptable where computers are not.
That of course makes it easy to not look up rules. You can decide on a temporary rule in the moment, and move on. That's a powerful option to have available to you. But it's equally powerful to have the actual rules available for reference. You can read a rule, as written, to make up for that other, less desirable aspect of humans when compared to computers: Imperfect and hazy memories. When you can't remember a rule, you don't have to spit out a 404 Page Not Found error. You can look it up.
Without rules, a roleplaying game wouldn't be a game, but it also wouldn't be a setting. It would just be a story, which can admittedly be fun with the right group but it's certainly not why I play games. I enjoy the research of finding the paragraph that specifies how something is intended to work, and I relish the conversations about how it might work differently, given the right set of circumstances.
My fondest early group gaming memories are of those moments. When I started playing roleplaying games with other people, the roleplay part of the game wasn't new to me. I'd already roleplayed as Lone Wolf and Black Baron and a bunch of other solo game book heroes. What I hadn't done was discuss the game world with other people. I hadn't asserted my ideas of how something might work and then had someone else with totally different ideas make a counter-proposal. It was exhilarating, and I still remember the moment when I suddenly realised I was playing D&D. It wasn't because I was kicking in doors and killing monsters, but because we'd stopped "playing" to look up rules and to theorycraft what impact those rules had on our game world, our characters, and the way we played the game.