Elon Musk, the SpaceX and Tesla exec, is famously demanding ' making meetings with him trial by fire."You can always tell when someone's left an Elon meeting,"shares an anonymous Quora userwho claims to have been working as an engineer at SpaceX for five years. "They're defeated," the anonymous engineer says, because Musk isn't afraid "to throw out six months of work because it's not pretty enough or it's not 'badass' enough."Thus the emphasis on thorough preparation."When we met with Elon, we were prepared," shares another anonymous Musk employee. "Because if you weren't, he'd let you know it. If he asked a reasonable follow-up question and you weren't prepared with an answer, well, good luck. Our discussions were efficient, to the point, and based in fact."Put another way, Musk demands that his employees use a way of reasoning that he picked up in his studies of physics: first principles thinking."I think it's important to reason from first principles rather than by analogy," Musk said in an interview with Kevin Rose."The normal way we conduct our lives is we reason by analogy," he said. "[With analogy] we are doing this because it's like something else that was done, or it is like what other people are doing. [With first principles] you boil things down to the most fundamental truths ' and then reason up from there."While he said"it takes a lot more mental energy,"the results tend to be more innovative, since you're starting fresh rather than building on what's been done before.This kind of thinking was crucial for the start of SpaceX.When Musk and his team were trying to estimate how much the first SpaceX rockets would cost, they could have just looked at the products on the market. But as the 99u blog points out, his team didn't settle for that analogy-based argument. Instead, they figured out what the necessary parts of a rocket are and then found out how much the raw materials of those parts would cost.The result was startling ' SpaceX could build a rocket for about 2% of the typical price.The takeaway: If you're called into a meeting with Elon Musk, you need to be thoroughly prepared, and you need to understand your topic from the first principles up.SEE ALSO:11 Tricks Steve Jobs, Jeff Bezos, And Other Famous Execs Use To Run MeetingsJoin the conversation about this story Click here to read full news..