SpaceX CEO Elon Musk has a history of setting sky-high expectations and taking over projects himself — something some employees have learned the hard way.

According to a 2015 authorized biography by Ashlee Vance, the "absolute worst" thing that a SpaceX employee can do is tell Musk that whatever project or task he's requesting is impossible.

SpaceX's culture values hard work and an ability to get things done, Vance writes. Employees who wait for detailed instructions, need hand holding or crave feedback could be in for some tough conversations.

Employees who tell Musk there's no way to get the cost down on a project or say that Musk's deadlines don't give them enough time, could soon come to regret it. The CEO will simply respond, "Fine. You're off the project and I am now the CEO of the project. I will do your job and be CEO of two companies at the same time. I will deliver," Brogan BamBrogan, a former SpaceX engineer, tells Vance.

Even more surprising, says BamBrogan, is that Musk manages to fulfill that promise. "Every time he's fired someone and taken their job, he's delivered on whatever the project was."

Some investors may disagree that those lofy goals are always met. At both SpaceX and Tesla recently, Musk has taken heat for missing ambitious product delivery dates.

These ambitious deadlines stem from Musk's eternal optimism, according to Vance. It's as if Musk plans "based on the idea that things will progress without a flaw at every step and that all members of his team have Muskian abilities and work ethics."

Asked about his approach, Musk says that he doesn't intentionally try to set impossible goals, in part, because he thinks they're "demotivating."

"You don't want to tell people to go through a wall by banging their head against it," the CEO tells Vance. "But I've certainly always been optimistic on time frames."

When it comes to delivering on products, you generally want to have a timeline in mind so that you're working toward something, explains Musk. While circumstances may arise that deter those projections, he says, "it doesn't mean that you shouldn't have tried to aim for that."

This article has been updated to clarify that employees could be taken off projects at SpaceX.

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