The number three seems to have a strong cognitive effect. Hearing something three times can help someone remember it, we usually need at least three observations to predict a pattern, and we seem to be able to easily remember about three things about a subject. Listing sets of three is a classic speech and rhetorical device for this reason.
It may be that slightly fewer than or slightly more than three would be a more accurate description of the cognitive relationship, but “The Rule of Two to Five” doesn’t make for such a good article title or simple guideline.
This can have some useful implications with regard to setting and scenario design. I’m sure it’s no coincidence that three primary ones come to mind almost immediately.
I have found that often when there are fewer than three points of interest to an entity in a scenario or setting the entity may be seen as unimportant. Conversely, many more than three can lead to a “tl;dr” situation where the entity may be treated as uninteresting because it is simply “too big”.
Three points of interest, on the other hand, suggests that the entity is important (the designer spent time coming up with three things!) without being too big to comprehend. It is a good balance point.
For similar reasons, I have read that when describing something (whether in an RPG scenario or in fiction) that you want to be noted you should describe the entity using three senses. Too few and it does not become interesting, too many and it becomes boring.
I have found that it often takes three pieces of information to make a decision. There is an old saying that runs something like “once is a fluke, twice is coincidence, three times is enemy action”. It often takes three observations to accumulate enough information to discern or confirm a pattern with confidence.
Justin Alexander has something he calls the “Three Clue Rule” (quoting below from the linked, very good article):
For any conclusion you want the PCs to make, include at least three clues.
He also says in his Node-Based Scenario Design essay that the Three Clue Rule can be inverted:
If the PCs have access to ANY three clues, they will reach at least ONE conclusion.
In the context of Justin’s essay this is reasonable – given three clues the players can come up with a choice of direction to explore next. I frankly think it unlikely that ‘any three clues’ will necessarily lead to a conclusion, if they are not obviously related, but can accept that three is likely to be sufficient to make a decision regarding next steps.
Freedom of Choice
I have found that players enjoy the game most when they have a moderate number of options available at decision time. Too few, a scenario can feel too linear and the players railroaded, but too many can give the feeling of a lack of direction.
Frankly, I have had more complaints from players because they “don’t know what they need to do” than “we’re being pushed in a certain direction”. I don’t doubt this is partly because I have a habit of being too subtle with my clues and hints, but I am also convinced that this can be more because I tend to be extremely flexible in what I consider ‘valid directions’. My players have in the past been less interested in figuring out the ‘correct direction’ than in ‘choosing a good direction’; constraint and clear path marking toward their goals can help that.
The number three has strong cognitive effects. I make use of this fact in my setting and scenario design practices, which I will describe in another article to come soon.