The Builders

They rummaged in the ruins of Earth's cities, looking for plans to restore vital machinery. But what they finally constructed got up and ran away!
Markten flew low over the sun-lit ruins, and wondered idly if he would find any more in them than he had found elsewhere on the planet.
Looks as completely dead as all the rest, he said to his companion. New City has a big enough population anyhow, as far as I'm concerned. Not that it's important, I suppose. There's always plenty of space in which to expand, but you know what I mean.
The younger occupant of the low-circling aircraft nodded his understanding. There'd be enough room on either side of the Big Mountains to take care of millions more of us, I guess. But I think you're right. Anyway, there isn't another nomad or ruin-dweller on the planet. New City is as complete as it's going to be—and as you say, twelve million is enough. But do you think we'll find any more plans down there?
Hard to say, Markten answered, levelling off the aircraft for a landing. But if there are traces of anything, I hope you'll keep your attention on what's of technical value and not waste time again on all that other stuff. None of us have ever bothered reading it—you can't build anything from it—no diagrams. To build is the only purpose of New City's civilization—how could anything else be of importance?
I've wondered off and on about that. But then, there is so little of anything left that it doesn't make much difference. Important thing is to find more diagrams.
Glad you realize it. I've been a citizen of New City ever since the first few of us on this continent started building it forty years ago, and I can tell you, building things is all that's important. You'd realize that soon enough if you'd wandered around, alone and useless, as I and a lot of other Elders did for years. Markten brought the fast, twin-engined aircraft in to a perfect landing, cut the power, and set the brakes. The two left their seats and started getting field equipment together.