Elon Musk says he's an unrelenting optimist. Warren Buffett made a similar point about the Tesla chief's vision and drive.

• Elon Musk described himself as relentlessly optimistic during a recent appearance.
• He's a dreamer who tries to solve impossible problems, Warren Buffett and Charlie Munger said.

Elon Musk recently described himself as "pathologically optimistic," underlining Warren Buffett's view that the Tesla, SpaceX, and Twitter chief likes to dream big and tackle insurmountable challenges.

"I guess I have somewhat of a pathological optimism," Musk said during Tesla's investor day last week, according to a transcript provided by AlphaSense/Sentieo. "Who would try to do this and rockets if they weren't pathologically optimistic?"

The electric-vehicle and space-transportation pioneer was standing by his prediction that Tesla will enable autonomous driving in several million of its cars by the end of this year. Musk hailed the hypothetical moment when a global fleet of self-driving taxis is enabled as potentially the biggest increase in asset value in history.

Buffett and his business partner, Charlie Munger, praised Musk's singular vision during Berkshire Hathaway's annual shareholder meeting this month.

"It's a dedication to solving the impossible and every now and then, he'll do it," the famed investor and Berkshire CEO said.

"He would not have achieved what he has in life if he hadn't tried for unreasonably extreme objectives," Buffett's right-hand man and Berkshire's vice-chairman added.

In contrast, Buffett and Munger said they seek out far simpler things to do in business.

"Warren and I are looking for the easy job," Munger said. "We don't want that much failure."

"If we can do it playing Tic-Tac-Toe, we'll do it," Buffett added.

Moreover, Buffett underscored the value of pessimism in Berkshire's key insurance business during Berkshire's shareholder meeting in 2013. Expecting the worst helps ensure the company puts aside plenty of money for emergencies, doesn't take excessive risks, and can weather any unwelcome surprises.

"We have a general tendency to be pessimistic in our assumptions about the likelihood of natural catastrophes," Buffett said.

The Berkshire bosses and Musk have discussed one another several times over the years. For example, Buffett and Munger have both praised Tesla's unlikely success in the brutal auto industry. Meanwhile, Musk has teased the pair that they could have invested in Tesla in 2008 for a tiny fraction of its current valuation.