There's another key here: both those industries were calcified with few innovators, so they had large latent pools of super-talented people that had been previously under-utilized.
By offering a compelling vision, Elon has sucked up much of the top talent in the space industry who had just been waiting for someone to come along with an uber-cool program for them to work on. His vision is so cool, in fact, that they are willing to work for much lower wages than they would make at a big defense contractor.
Similarly with Tesla, there was a large pool of talented engineers who are passionate about electric cars, who had just been waiting for the right company to come along and rescue them from dead-end projects at the big car companies.
This is very true - for example, his VP Propulsion Development, Tom Mueller, spent 14 years as a rocket product manager at TRW, and spent 6 years leading a team of 80 engineers developing a candidate engine for the Delta IV, and winning plaudits like a chairman's award for technical excellence but without anything he worked on actually getting launched. I can't imagine how gratifying it must feel for him now to watch things he made flying into orbit and opening access to space. It's hard to beat that kind of real accomplishment as a job perk.
Elon: "It's important enough to be on the scale of life itself, and therefore goes beyond the parochial concerns of humanity," Musk says of our interplanetary destiny. "We're all focused on our little things that are of concern to humanity itself. People think of curing AIDS or cancer as being very important, and they are—within the context of humanity. But curing all forms of cancer would improve the average life span by only two to three years. That's it."
"In other words, while eradicating disease is a worthy pursuit, and would extend the lives of individual human beings, my life's work is extending the life span of life itself."
1. VTOL supersonic electric jet: fast, quiet, low-cost to operate (what he jokingly referred to in Iron Man 2, IIRC)
2. Prefabricated metal sections for creating a double-decker/box highway, that could be dropped in place like a lego system with minimal disruption to traffic.
3. Fusion problem, magnetically-confined fusion, gets easier as you scale it up.
By offering a compelling vision, Elon has sucked up much of the top talent in the space industry who had just been waiting for someone to come along with an uber-cool program for them to work on. His vision is so cool, in fact, that they are willing to work for much lower wages than they would make at a big defense contractor.
Similarly with Tesla, there was a large pool of talented engineers who are passionate about electric cars, who had just been waiting for the right company to come along and rescue them from dead-end projects at the big car companies.