It's more like this: you've been on dozens and dozens of hiking trips. Except these trips generally go through seismically unstable territory and war zones. You

It's more like this: you've been on dozens and dozens of hiking trips. Except these trips generally go through seismically unstable territory and war zones. You just never know when you'll have to dig a tunnel underneath a battlefield to get to the next river you'd have to cross — a river unmarked on your map, or perhaps the result of some aggressive "engineering" by someone since your map was drawn. Then you get an urgent message from your customer: you weren't supposed to hike from SF to LA after all. You actually need to go from New York to London, on a submarine. Specs require that you do this without surfacing or refueling. So you need to design a nuclear reactor, figure out a way to put it on the leaky old U-Boat your customer just happens to have lying around. All within the same timeline as before, and in the same budget. You've had all this happen to you a few dozen times, so you factor in the time you know you need to build submarines (all just different enough, of course, that you can't reuse parts, even if the customers let you adapt, say, the propeller shafts to a new customer's design: I hear that in software, this is called "DRY" and "using libraries and frameworks" and "refactoring") — and you give an honest estimate: "it'll take eight months of full-time work, and will cost you about X hundred thousand dollars (a bargain for a nuclear submarine, if you ask me)" — and the customer will then go to someone else, leaving you wondering how you'll pay your bills.