When you tell a story, you often use the rule of threes. Three bowls: Daddy Bear’s porridge is too hot, Momma Bear’s is too cold, Baby Bear’s is just right. If you were to only be told about Daddy Bear’s hot porridge, you’d think that to be a simple fact of the story, just as irrelevant as the color of Daddy Bear’s hat. It just *is*. If you were told also about Momma Bear’s porridge, you could make the connection between the two bowls. They’re both are “too [relative measure of temperature].” With the inclusion of Baby Bear’s bowl, you could rightly assume that the temperature of bowls owned by bears is important to the world in some way. Now in a story, three has a sense of completeness about it. In a joke, the third element is often the twist, the one that breaks the pattern and your expectations in a humorous way. This rule of three is embedded somewhere deep in us.
“Once is Unique, Twice is Pattern, Thrice is Law”
This phrase is a rule of player psychology I’ve come to internalize. When running a roleplaying game, we GMs often think about how things are presented to the players. As the only source of sensory information to the players, what we say shapes how they react in a major way. One of those factors that affects presentation is frequency.
For example, I was running the fantastic, cannot-be-recommended-enough, Tomb of the Serpent Kings in my Hot Springs Island game (10 sessions in using Maze Rats 5.3. Having a great time, thank you). One of the doors early in the dungeon contains a hammer trap that deals significant damage that may outright kill a PC. When the PCs found a different entrance later in the dungeon, they found another hammer trap. “Ah, this trap repeats” one of my players said. “There may be more.” It was simple recognition of a pattern: some doors have hammer traps.
Now what if the VERY next door contained a hammer trap? On a third time, it’s pretty safe to assume that ALL doors are trapped. I wouldn’t be surprised if players just refused to open doors after that.
What’s the point? How often things happen is a powerful tool. Use it well to establish continuity and relationships between places, factions, and monsters.