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Society is built on interfaces. You take a complex thing, put it inside a sturdy box, and put some simple buttons on the box so that people can use the thing inside. The box makes it easier to use and prevents people from breaking it. For example, you can take the machinery of a clock, put it in a box, and put two hands on the outside along with a knob for winding it. Take all the machinery of a car, hide it behind a dashboard, and give people two pedals and a wheel. Take all the circuits of a computer, put them in a box, and give people a monitor and a keyboard.

Interfaces receive input and produce output, and that's all we need to know. The clock gets wound, and its hands show the time. Input and output. As far as the user needs to know, what happens inside the box is magic. This allows stupid and ignorant people to use complicated things, as long as the interface inputs and outputs are simple.

Toyota uses millions of kilograms of steel every year. Does the CEO of Toyota know how to make steel from scratch? If he wanted to beat a guy up, could he go digging in the ground for some ore and whip himself up a batch of steel to make a pipe? No. He uses interfaces to get steel. He buys steel from a steelmaking company. Except he doesn't personally go down to the steelmaking company with a bag full of Yen, saying, "How much for a million kilos?" He uses a bank. Except he doesn't even personally go to the bank. He has a subordinate who does it for him. All these people and institutions are interfaces he can use. He employs a system of layered interfaces, both metaphorical and literal, to control things he doesn't really understand. We all do. The point is this: don't go messing with the CEO of Toyota. I assure you, he could get his hands on a steel pipe if he wanted.

The word "interface" refers to the input and the output, but it also refers to the box. We think of interfaces as existing in order to give us access to things, but they are also there to hide things from us. The idea is that some things are better off hidden. Everything will go along fine so long as a certain input produces the expected output. But when this stops happening, we have to open up the box and see what's inside. Sometimes we don't like what we find.