We have a lot of unwritten rules in Table Top RPG land. Each group has their own collection, and various subgroups and niches have variations on them. In the land of GM advice, one of the most commonly bandied about tropes is that as the GM you should never say no to your PCs. You should say "yes, if...," "yes, and...," or "yes, but..." but you shouldn't say no. But what does that really mean? Can you really not say no? Today I want to look at this piece of advice a bit closer, break it down, and suss out the core wisdom it is trying to impart.
The rule itself is advice for GMs to help them with dealing with PCs and some of the crazy plans they come up with. Over the course of a standard table top game your PCs will do everything from commit heists, plot out regicides, dispose of evil (or good) fairy queens, and retrieve the staff of power from the abyssal witches of time...and that's even if you're running a game about being farmyard animals trying to win the blue ribbon at the town fair.
The rule is meant to govern your initial response when your player asks about something zany. For example, if you put a tome of ancient horror and evil in front of your characters and someone asked if they could translate it, your first impulse would likely be to say "no." After all, translating the tome is a major part of your plot, and could do all sorts of unspeakably bad things. Plus it is an ancient language that the player has no way of knowing. This rule is specifically for that situation, because in that situation you shouldn't say "no" but one of the three choices. "Yes, and it will take a really long time," or "Yes, but you will have to roll exceptionally well" or "Yes, if your character first learns the ancient tongue the book is encoded in."
The Heart Of The Rule
The core of the rule is about not denying your players opportunities. Just because your story "wants" that ancient tome to stay untranslated doesn't mean that it needs to be. In fact, if you're doing an RPG right the players should be able to do it if they try hard enough. Maybe they'll fail, or maybe they'll succeed and in doing so doom the world. That's fine either way.
However, the point of this rule isn't about your players running rough shod over your world either. It is about creativity and remembering that RPGs are cooperative storytelling games. Even in a GM vs. PC game, ideally the story should be one crafted by the GM with their control of trhe world and NPCs working in conjunction with the players who control the focal characters.
So Just Don't Say No?
This is where it gets dodgy. Because there are times you have to say no. Some things are just impossible. If you're running a realistic modern day game, then no matter how hard a player tries they're not going to be able to fly like Superman just because they want to. Other things may actually be impossible for other reasons.
However, "no" should never be your first answer, and this is what the rule is getting at. If a player asks if they can do something - and they're not just being silly - then that idea should be considered thoroughly. Is what they want to do actually impossible, or merely improbable? As a hint, if something later in the adventure is going to make it possible than the answer is "yes, it is possible." Hell, unless something goes against the actual fundamental laws of the universe, it should be possible. It can be hard, but it should be possible.
So What Do I Do?
So what do you do when your player wants to do something zany? Embrace it. Figure out what would need to happen for them to hae a chance and let them know some basic idea of it. If the player is sereious about it, they'll go off to accomplsh their thing which means...you know what your next several sessions are going to be about.
The ancient tome the PCs want to translate? They need to figure out how to open it (quest 1!) they need to learn the language (quest 2!) They need to figure out the key for decoding the book (quest 3!) and then they can decipher it. Those 3 quests could be used to guide them along the planned adventure, or to broaden the adventure that is already there.
But lets say the PCs want to stop the assassins coming after them. Impossible? Not really. I mean, they could learn about the assassin order, find out how they work, and use those rules to gain freedom. Or they could kill all the assassins, or as many as needed to end the contract. Or they could a lot of things.
However, sometimes things the players want may be impossible and that is ok. A player trying to stealthily cast a spell when no one is in a room may simply never get that opportunity because of what is going on around them. A player searching desperately for a weapon in a jail house may be unable to find one if the place was stripped clean of all tools. Someone with no magical ability in a world with no magical eye glasses may actually not be able to read a tome written in magic ink. It sucks, but it can happen. It just shouldn't happen often, and the word "no" should never be your first answer, no matter how knee jerk a reaction it may be.