Sleep isn't just something we spend a lot of time doing. It's also something we spend a lot of time thinking about. Sleep deprivation can cause a variety of problems that can negatively affect your productivity, leading to anything from concentration problems to depression. But what is the right amount of sleep? The traditional number (and the National Sleep Foundation's recommendation) is somewhere between seven and nine hours for a healthy adult. However, some experts argue that anything more than seven hours is unhealthy. Furthermore, the C.D.C. found that some people may have a gene that lets them sleep less. Take to the internet or hit the books when it comes to sleep and you'll find a lot of disagreement, conflicting studies, and not too many clear answers. One thing is clear, though: Sleep is important.

Some of history's most successful people--and some of the most successful people living today--have answered the sleep question in surprising ways. While some, like Bill Gates, Warren Buffet, and Amazon founder Jeff Bezos, get between seven and nine hours of sleep every night, others have strange habits and schedules that may seem impossible to keep to the average sleeper.

Donald Trump

According to Donald Trump, you don't get to be a celebrity, business magnate, real estate tycoon, and presidential candidate without sacrificing some rest. Trump credits his success, in part, to the fact that he gets only three to four hours of sleep each night. He's said, "How does somebody that's sleeping 12 and 14 hours a day compete with someone that's sleeping three or four?" For some reason, possibly genetic, this dearth of sleep doesn't run Trump into the ground with exhaustion. On the contrary, it seems that the proof is in the pudding with Trump's sleeping habits.

Thomas Edison

Thomas Edison, one of history's most famous inventors, would not be sympathetic to discussions of healthy sleeping habits. Edison simply had too much he wanted to accomplish, and he considered sleep a royal waste of time. Like Trump, Edison got only three--sometimes four--hours of sleep a night, although he was known to occasionally take a power nap during the day. Allegedly, Edison once worked a full 72 hours straight, without any breaks for rest. Who knows, maybe part of Edison's inspiration for inventing the light bulb was so that he could work late into the night with adequate lighting?

Marissa Mayer

Marissa Mayer, currently the CEO of Yahoo and previously the renowned Google executive, gets very little sleep. It should come as no surprise--considering that she infamously worked as much as 130-hour work weeks while at Google--that Mayer prioritizes work over rest. She reportedly gets only four to six hours of sleep every night, recharging by taking week-long vacations about three times every year.

Martha Stewart

Whatever you think of Martha Stewart, she's a woman who needs no introduction. Stewart has achieved an astounding amount, and she hasn't done it by sleeping. Somehow, household name Martha Stewart manages to not just get by, but also to thrive, on four hours or less each night.

Nikola Tesla

Nikola Tesla, one of history's other most famous inventors, apparently was able to one-up Edison in more areas than just technological advancements in electricity. At most, Tesla would get just two hours of sleep per night. As a boy, Tesla would secretly stay up all night reading without being visibly any worse for wear. Keeping this extreme a sleep schedule did contribute to a nervous breakdown in his 20s, but Tesla didn't become known as the Father of Electricity by quitting--or, apparently, by sleeping.