The Unity of the Rings
A ring's a thing without a beginning or end. Remember that, because rings are the second key to understanding the planes. Everything comes in rings. Sigil's a ring, the Outlands are many rings, the Outer Planes form a ring, the Elemental Planes form a ring - this is the way of the multiverse, understand?
On the Outer Planes, the Great Road is the band of the ring, and all the planes are its gemstones. Following the Great Road, Mechanus leads to Acheron, Acheron leads to Baator, Baator leads to Gehenna, and so on. By following the road, the order never changes.
On the side, the powers think in rings, too - circles upon circles of logic that never go anywhere. A body's always got to watch out for their endless snares.