Planejammer: Ad Astra Per Arcana
The Rule of Three
Things come in three. No one really knows why, but examples are found in the most fundamental aspects of the multiverse: Good, Evil, and Neutrality; Law, Chaos, and Neutrality; Inner Planes, Prime Material Plane, and Outer Planes; Prime, planar, and petitioner.
The number three seems to have some power to it, and things both good and bad tend to happen in sets of three on the planes. Planars who see two things know a third probably lies hidden beneath the surface, and more than one treatise has been written on the matter. Of course, that may just be the power of belief making what people already believe real, but the very shape of the Great Ring seems to prove there’s something to the Rule of Three.