"The tao that can be told is not the eternal Tao..."
When teaching something or when building something, you typically have some building blocks and you build some kind of structures from them by some similarly taught skills to achieve your goals in the building work. Learning things from books or in school is like this too.
So you have some single goal that you want to buikd something or to have the skill of building things like that. And that goal motivates you to spend some of your time in the building work or in studying it. So during those moments that single goal of building dominates your life, you are concentrated to that work and that takes away a large part of your energy from the other sides of your life.
But there are many things in life. Like walking on a street you can see different kinds of people, some houses, children playing, sights of gardens, cars driving, glimpses to homes, the weather, the feel of you walking, thinking of your day, social encounters, plants and animals etc. If you lift one of these to be a subject of conversation that still aren't your whole wisdom about how to live your life. With each skill you need the backing of a strenght and wisdom bought to you by healthy kind of life with a multitude of things and skills in it.
In school the most stupid ones are the ones who rely solely on school. The most intelligent ones are interested in life, in sports and arts and in social relationships, practical life with many things to do: they get added capacity from doing many kinds of things fullheartedly.