Legendary investor and CEO of Berkshire Hathaway Warren Buffett is worth upwards of $75 billion.
According to his friends and fellow billionaires, Bill and Melinda Gates, the secret to the octogenarian's success is his unceasing optimism.
"Optimism is a huge asset," Melinda Gates writes in the Bill & Melinda Gates Foundation's annual letter, addressed, this year, to Buffett. "We can always use more of it. But optimism isn't a belief that things will automatically get better; it's a conviction that we can make things better.
"We see this in you, Warren. Your success didn't create your optimism; your optimism led to your success."