LOS ANGELES—Revealing his vulnerable side in a starkly honest interview, an emotional Elon Musk recalled this week how he spent his entire birthday alone working on concepts for new ways to mistreat employees at the Tesla factory. “When you’re the CEO, the responsibility of developing innovative new ways of underpaying the workers falls to you, as does compromising their safety or punishing them for not meeting unrealistically high unit quotas, and sometimes that means sacrificing your personal life—even your own birthday,” said Musk, adding that it was very lonely staying up all night researching adhesive toxicity in order to increase exposure to harmful fumes among workers. “Yes, it would have been nice to spend my birthday with friends and family instead of holed up in the factory devising new ways for employees to be disfigured by clouds of caustic chemical vapor or seared by welding robots while they work 16-hour shifts to meet my insane 495 percent production increase. But I feel, as CEO and chief visionary, that I owe it to the guys on the line to see it all through to the end. Sure, I miss cake and candles; I’m not a monster. But if I don’t spend hours removing that ugly, restrictive yellow caution tape from the factory floor, or improvise a workstation ergonomics layout that encourages repetitive stress injuries, who will?” Musk claimed to take only small comfort in the knowledge that due to their remarkably long stints in either the factory or hospital, his employees were missing many important life events as well.