What books are for

Conversation with my youngest son on the way to his piano lesson.

With-a-Why: Hey, do you know the Pythagorean theorem?
Me: Yeah, of course. A squared plus B squared equals C squared.
With-a-Why: But do you know what that means?
Me: If you take the hypotenuse of a right triangle and square that number, then that should equal the sum of the squares of the two smaller sides.
With-a-Why: My math teacher said that it's the one math formula our parents would remember.
Me: (laughing) So he was right.
With-a-Why: Yeah.
Me: Well, I remember other math formulas too, but I like math, and a lot of people don't.
With-a-Why: He said everyone remembers the Pythagorean theorem.
Me: I think it's because of the Wizard of Oz.
With-a-Why: The Wizard of Oz?
Me: In the Wizard of Oz, when the Scarecrow gets the diploma, he says the Pythagorean theorem, except with an isosceles triangle instead of a right triangle. Isosceles is a cool word, so it sounds intelligent, but it makes the formula wrong. But that's why people my age know the Pythagorean theorem.
With-a-Why: Because of the Wizard of Oz?
Me: Yeah. You know the scene I'm talking about, right?
With-a-Why: Yeah. But that's not why people remember it.
Me: Sure it is.
With-a-Why: The Pythagorean theorem is awesome. That's why people remember it.
Me: Well, it is cool. If I close my eyes, I can picture all these triangles, lined up each with a right angle, and I sort of picture the sides of the triangle as a rope, so that you can move the rope and shift the sides of each triangle, and I can imagine that there would be a pattern to the way the shorter sides of the triangle relate to the longest side.
With-a-Why: It's cool how it works out. Every. time.
Me: Well, that's the reassuring thing about math formulas. It's nice that they stay the same.
With-a-Why: I like math because it makes sense.
Me: Yeah. Well, I like that too. There is so much in the world that doesn't make sense.
With-a-Why: Yeah. Like people hitting each other with little black pebbles at high speed.
Me: Little black pebbles? Who does that?
With-a-Why: (Looking at me sideways.) It happens all the time.
Me: Oh, you mean bullets.
With-a-Why: Yeah.
Me: Who calls them little black pebbles?
With-a-Why: The rabbits. In Watership Down.
Me: Oh, right. Well, I guess that's what books are for. For things that don't make so much sense.
With-a-Why: Yeah.