Here's Tom Mueller, the main rocket expert at early SpaceX, describing his experience working with Elon:

>And, uh, I’ve seen that hurt us before, I’ve seen that fail, but I’ve also seen— where nobody thought it would work— it was the right decision. It was the harder way to do it, but in the end, it was the right thing. One of the things that we did with the Merlin 1D was; he kept complaining— I talked earlier about how expensive the engine was. [inaudible] [I said,] “[the] only way is to get rid of all these valves. Because that’s what’s really driving the complexity and cost.” And how can you do that? And I said, “Well, on smaller engines, we’d go face-shutoff, but nobody’s done it on a really large engine. It’ll be really difficult.” And he said, “We need to do face-shutoff. Explain how that works?” So I drew it up, did some, you know, sketches, and said “here’s what we’d do,” and he said “That’s what we need to do.” And I advised him against it; I said it’s going to be too hard to do, and it’s not going to save that much. But he made the decision that we were going to do face-shutoff.

>So we went and developed that engine; and it was hard. We blew up a lot of hardware. And we tried probably tried a hundred different combinations to make it work; but we made it work. I still have the original sketch I did; I think it was— what was it, Christmas 2011, when I did that sketch? And it’s changed quite a bit from that original sketch, but it was pretty scary for me, knowing how that hardware worked, but by going face-shutoff, we got rid of the main valves, we got rid of the sequencing computer; basically, you spin the pumps and pressure comes up, the pressure opens the main injector, lets the oxygen go first, and then the fuel comes in. So all you gotta time is the ignitor fluid. So if you have the ignitor fluid going, it’ll light, and it’s not going to hard start. That got rid of the problem we had where you have two valves; the oxygen valve and the fuel valve. The oxygen valve is very cold and very stiff; it doesn’t want to move. And it’s the one you want open first. If you relieve the fuel, it’s what’s called a hard start. In fact, we have an old saying that says, “[inaudible][When you start a rocket engine, a thousand things could happen, and only one of those is good]“, and by having sequencing correctly, you can get rid of about 900 of those bad things, we made these engine very reliable, got rid of a lot of mass, and got rid of a lot of costs. And it was the right thing to do.

>And now we have the lowest-cost, most reliable engines in the world. And it was basically because of that decision, to go to do that. So that’s one of the examples of Elon just really pushing— he always says we need to push to the limits of physics. Like, an example I’ll give is, on the car factory; you know, a car moves through a typical factory, like a Toyota or a Chevy factory; a car is moving at you know, inches per second. It’s like, much less than walking speed. And his thoughts are that the machinery, the robots that are building the car should move as fast as they can. They should be moving so fast you can’t see them. That’s why you can’t have people in there, because they’d get crushed; people move too slow. That’s the way he thinks. “So, what are the physical limits of how fast you can make a car?” He looks at videos of like, coke cans being made, and things like that, where you can’t even see them; it’s just a blur. And, you know, the puck of aluminum, cut it up, deep-draw, fill it with coke, you put the lid on, you put the lid on it; it’s just like going down the assembly line so fast you can’t even see it. And Elon wants to do that with cars.

People often claim SpaceX was just Musk's show rather than a team effort where Mueller and Shotwell at least were just as important and probably more people besides. And he's had his share of bad ideas. But at the same time the sort of restless perfectionism he tries to get people to have in their engineering is a net force for good, similar to what Steve Jobs did with design at Apple.