“Maybe we’ll make a flying car, just for fun,” Elon Musk told the Independent back in 2014. The news outlet insisted at the time that Musk wasn’t joking and that he should be taken seriously, given his success with other companies like PayPal. At the time, the Tesla CEO was worth a measly $8.4 billion according to Forbes, a fraction of the $413 billion he currently holds on paper. But when a billionaire CEO says he’s going to do something, you’re supposed to hear him out. “We could definitely make a flying car—but that’s not the hard part,” Musk was...