There's a very good piece of adventure design advice that goes like this: you must leave at least 3 clues for something you want the PCs to do. As they could miss one, or even two, of these clues, you need to have enough there to point the PCs in the right direction. I wanted to talk about why this rule works, and give some advice about putting it in action.

As an initial matter, this rule isn't about getting the PCs from one room of a dungeon to the next room of a dungeon. They'll just walk that way anyway. This is about planting a clue to something the PCs can't otherwise know (such as to investigate the mill outside of town as the source of wererat attacks) or goes against what they'd otherwise do (such as to spare a bloodthirsty orc because he knows important secrets). For these things, you should put in at least 3 clues to guide the PCs.

First, this rule works because it reduces cognitive GM load. Think of it this way: in an adventure, the PCs don't need 3 clues. They need one. The 3 clues aren't built into the adventure for the PCs, they're there to help the GM get the PCs pointed in the right direction. Once the PCs have one of these clues, they usually just move on, and they might never know the alternate clues exist. The GM can just ignore them, and the adventure keeps rolling. It is substantially easier for the GM to simply ignore 2 undiscovered clues than to invent more clues on the spot if the PCs miss the single clue the adventure provides. Adventures exist to reduce GM cognitive load--something I'll talk about another time--and this is an example of how a well-built adventure aids the GM rather than force him to do more work.

Sometimes, the PCs are being particularly thorough, and they might get the same clue a couple of times. This is a good thing--it acts as a reward for the players to let them know they're on the right track. The confirmation of what they've already discovered solidifies their path. So PCs finding extra clues isn't bad. I've heard some PCs say immersion-breaking things like, "Man, the adventure REALLY wants us to go to that abandoned mill" if they find all 3 of the seeded clues. But even this peek under the hood of the adventure's design seems like a win to them--they've outsmarted the adventure in this small way.

Second, these clues should differ in source. A note from the mastermind in the alchemist's shop is fine, but three different notes isn't likely to be much more effective and strains verisimilitude. As a general rule to provide your three clues, keep the following in mind: one should be delivered by a trustworthy NPC, one should be delivered by an antagonist NPC, and the third should be a purely physical clue. Not only does this plant 3 clues, but it plants them in ways likely to resonate with the PCs in different ways.

Some examples? Sure! Let's say the PCs need to learn about the mastermind in the alchemist's shop. They otherwise don't have any reason to suspect that location, but the adventure needs to send them there.
* First, they might discover a person that escaped from the alchemist's shop and is hiding out. This sympathetic NPC asks the PCs to check it out.
* Second, they might fight one of the mastermind's villains, and he bears a note from the mastermind with alchemical stains that could only come from the alchemist's shop.
* Third, the alchemist's shop might have put on nightly displays of fireworks or other whiz-bang expositions to delight the neighbors every third day, but these haven't occurred in the past week and the shop has been unexpectedly closed. 

They're off to the alchemist's shop, and the adventure keeps rolling!

(This blog's title has nothing to do with the wizened NPC named Rule-of-Three from Planescape, but I thought of him as soon as I wrote the title.)