There are certain commonalities among the world’s richest people.

After studying wealthy people for over five years, author Thomas C. Corley pinpointed a hallmark of the rich: positivity.

“Long-term success is only possible when you have a positive mental outlook,” he writes in his book, “Change Your Habits, Change Your Life.”

On the flip side, negativity can be detrimental to your success, Corley found. After all, there’s a reason the rich avoid pessimists.

The problem for most people is that they’re completely unaware of their thoughts, positive or negative, he explains: “If you stop to listen to your thoughts, to be aware of them, you’d find most of them are negative. But you only realise you are having these negative thoughts when you force yourself to be aware of them. Awareness is the key.”

He’s not the only one to suggest that positivity is a key to wealth and success.

Nearly a century ago, journalist Napoleon Hill drew similar conclusions. After researching over 500 self-made millionaires, he found that they were all likeable — or, in today’s lingo, they all had “soft skills” and a high level of emotional intelligence.

As he wrote in his 1937 classic, “Think and Grow Rich,” “There is no hope of success for the person who repels people through a negative personality. Success comes through the application of power, and power is attained through the cooperative efforts of other people. A negative personality will not induce cooperation.”

Corley and Hill’s conclusions are backed by science — as research shows today, positive, happier people are more likely to perform better at their jobs and are less likely to be unemployed.

Need a push on your journey to optimism? Check out nine science-backed ways to immediately boost your mood, and read why billionaire investor Warren Buffett says he’s such an optimist.

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