One of the most important lessons Milo learned on his journey came from a mistake rather than a success.
He had turned the wrong way at a fork and ended up in a place called the Doldrums instead of moving forward.
The Doldrums were inhabited by Lethargarians who did nothing all day and discouraged thinking of any kind.
Milo nearly got stuck there himself before Tock the watchdog arrived and helped him escape by thinking carefully.
The experience taught him that wrong turns were not simply problems — they were also sources of information.
He learned what the Doldrums felt like and why people ended up there and how to recognize the warning signs.
That knowledge, earned by going the wrong way, served him better than a smooth road would ever have done.
Even wrong roads lead somewhere.

The Phantom Tollbooth's treatment of mistakes and wrong turns reflects a genuinely sophisticated educational philosophy.
Most narratives about learning treat errors as things to be minimized, corrected, and moved past as quickly as possible.
Juster's story suggests instead that wrong turns are often the most information-dense parts of any journey.
The Doldrums, the Island of Conclusions, the Valley of Sound — Milo arrives at all of these by making mistakes.
And yet each of these places teaches him something that the correct path, by definition, could not have taught him.
The Island of Conclusions, reached by jumping to them carelessly, shows him exactly what that habit costs in practice.
The Doldrums, reached by not thinking, shows him what happens when thinking is abandoned as too difficult or too uncertain.
A straight road to the destination would have delivered Milo faster but returned him essentially unchanged and unequipped.
Even wrong roads lead somewhere.