The Lands Beyond are set in a stable time loop
- When Milo leaves the world, he hears the Mathemagician and King Azaz start their argument again, which means the Lands Beyond is going to be thrown into another war, which means an outsider needs to step in and sort things out. And then when the said outsider leaves, the war is set up to start again, causing a cycle to be set up. This is reinforced by the letter Milo gets, which says other people need to use the Tollbooth too.
Milo wasn't just bored at the start of the story...he was depressed.
The opening narration of book describes him as being interested in nothing, "least of all the things he should have." Anhedonia—an inability to take pleasure in things you would normally enjoy—is a key symptom of clinical depression. Fortunately, the Tollbooth caught his condition while it was still mild, and the shift in perspective jump-started his recovery.- Except depression can't be cured just with having some variety in your life.
