In his 2015 book, "Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future," Ashlee Vance shares the story of how Musk stopped working with his longtime executive assistant in early 2014.

According to Vance, the assistant, Mary Beth Brown, asked Musk for a significant raise after she'd been working with him for 12 years. In response, Musk told Brown to take two weeks off, during which he would assume her responsibilities and see whether she was critical to his success.

When Brown returned, Musk told her he didn't need her anymore.