Grant Cardone didn't always have millions in the bank. At age 25, he was deep in debt and stuck in a sales job he hated .

The entrepreneur, who owns and operates four companies that do nearly $100 million in annual sales, reached seven-figure status by putting in more hours, he writes on Medium: "Most people work 9 to 5. I work 95 hours (per week). If you ever want to be a millionaire, you need to stop doing the 9 to 5 and start doing 95."

He's not the only self-made millionaire to say that the steady salary that comes with a 9-to-5 job is holding people back from getting rich.

Steve Siebold, who also spent 25 years studying wealthy individuals for his book "How Rich People Think," notes that there is a critical difference in how the wealthy and everyone else choose to get paid: Average people choose wages based on time — an hourly rate, for example — while the rich are typically self-employed and get paid based on results.

"The masses almost guarantee themselves a life of financial mediocrity by staying in a job with a modest salary and yearly pay raises," Siebold writes.

They "wait on the sidelines, terrified to get in the game for fear they will lose the little money they have. Meanwhile, the world class is earning more in a year than the average person will make in a lifetime."

If you want massive success, you have to focus on earning and be prepared to grind, Cardone says. And once you do start seeing financial gains , don't change your mentality: "If you gave me $5 billion, I'd still be grinding tomorrow.

"My life is not in the stands. My life is not as a spectator. My life is being a player on the field."

Remember, "there's no shortage of money ," Cardone writes. There's just "a shortage of people doing 95 hours each week."

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