from wikipedia "In late 2001, Mueller began developing a liquid-fueled rocket engine in his garage and later moved his project to a friend's warehouse in 2002.[1] His design was the largest amateur liquid-fuel rocket engine, weighing 80 lb (36 kg) and producing 13,000 lbf (58 kN) of thrust.[1] His work caught the attention of Elon Musk, PayPal co-founder and CEO of Tesla Motors, and in 2002 Mueller joined Musk as a founding employee of SpaceX."
that's a hell of a lucky find by Musk and a hell of a roll of the dice by Mueller. Around the same time is when Shotwell joined, she's equally incredible but in a different way. i don't now how Musk found her.
Even then, what followed has been black swan territory. Every major development announcement at SpaceX is met with "you're crazy" and laughter from the industry and yet, a few years down the road, there it is working. Again, i really want to know what went so right.