One reason was that rocket components were subject to hundreds of specifications and requirements mandated by the military and NASA. At big aerospace companies, engineers followed these religiously. Musk did the opposite: he made his engineers question all specifications. This would later become step one in a five-point checklist, dubbed the algorithm, that became his oft-repeated mantra when developing products. Whenever one of his engineers cited a requirement as a reason for doing something, Musk would grill them: Who made that requirement? And answering The military or The legal department was not good enough. Musk would insist that they know the name of the actual person who made the requirement. We would talk about how we were going to qualify an engine or certify a fuel tank, and he would ask, Why do we have to do that? says Tim Buzza, a refugee from Boeing who would become SpaceXs vice president of launch and testing. And we would say, There is a military specification that says its a requirement. And hed reply, Who wrote that? Why does it make sense? All requirements should be treated as recommendations, he repeatedly instructed. The only immutable ones were those decreed by the laws of physics.

Elon Musk by Walter Isaacson