"Physical, psychological, and emotional comfort is the primary goal of the middle class mindset." 
It's a concept that's been around for nearly a century - journalist Napoleon Hill introduced the psychological barriers preventing many of us from getting rich 78 years ago - but is still more than relevant today.
In a more recent study, of over 1,200 of the world's wealthiest people, self-made millionaire Steve Siebold uncovered similar findings, which he details in his book, "How Rich People Think."
He noticed something surprising throughout his research: Rich people find comfort in uncertainty.
Meanwhile, the average person finds peace of mind in familiarity, and hesitates to leave their comfort zone.
This desire for comfort comes at a cost.
"Physical, psychological, and emotional comfort is the primary goal of the middle class mindset," Siebold writes. "World class thinkers learn early on that becoming a millionaire isn't easy and the need for comfort can be devastating. They learn to be comfortable while operating in a state of ongoing uncertainty."
If you want to get rich, you have to be OK with being uncomfortable. If you're not, learn how to be, Siebold advises: "The great ones know there's a price to pay for getting rich, but if they have the mental toughness to endure temporary pain, they can reap the harvest of abundant wealth for the rest of their lives."
Start adopting this mindset today with one of Siebold's suggested strategies: "Make a list of the five things you must do today that are uncomfortable but will help you build your financial fortune."