Elon Musk's advice to Jeff Bezos: "Contour less, work harder.

Jeff Bezos and Elon Musk are locked in a 15-year feud over each other's space ambitions... Elon Musk recently shared his thoughts on Jeff Bezos on Twitter. When asked by a follower if he thought the Amazon founder was a "nice guy," the tech billionaire said, "I think he's doing just fine.

The world's richest man also has tips for the third richest person: "If he wants to go into orbit, fewer coupons and more work will be suggested."

Musk refers to the space race between them. Jeff Bezos and Elon Musk have been embroiled in a 15-year feud over their space ambitions, with the two companies competing and reportedly fighting alone, Business Insider reports.

Musk owns SpaceX, and Bezos owns Blue Origin. While Musk is focused on sending humans to Mars, Bezos wants to send humans to the moon. The fierce rivalry between the two most potent CEOs started in 2004 when Blue Origin and SpaceX were still in their infancy. Musk and Bezos met to discuss their respective ambitions for a reusable rocket, and things were not going well.

"I did my best to give good guidance, which he largely ignored," Musk said after the meeting, according to Christian Davenport's book, The Space Barons.

The only time the two billionaires got things done was probably in April, when Musk said he was seriously considering turning Twitter's San Francisco headquarters into a homeless shelter after becoming the company's controlling shareholder.

In response to Musk, Bezos suggested using "parts" such as Amazon's use of its Seattle headquarters.