If financial success is your goal -- and most of us include some degree of wealth in our individual definitions of success -- your personality definitely plays a role. (According to a 2018 study, rich people possess these five personality traits.) 

But so does how you answer one simple question. 

Rafael Badziag interviewed 21 self-made billionaires while writing The Billion Dollar Secret: 20 Principles of Billionaire Wealth and Success.  

Some credited a willingness to take intelligent risks. Some credited the self-determination spirit of "If it is to be, it's up to me." Others credited relentless self-improvement, ignoring naysayers, and embracing an appetite for hard work.

But what did they all have in common? They all answered one question the same way.

"What do you enjoy more: making money, or spending it?"

According to Badziag, "The difference between financially successful people (millionaires) and financially super successful people (billionaires) boils down to the fact that the latter get pleasure making money but don't enjoy spending it."

Granted there are exceptions. Take Mukesh Ambani, whose 27-story, 400,000-square-foot "home" in Mumbai is worth an estimated $1.2 billion.

Clearly, Ambani is willing to spend a little money. But, then again, he's worth an estimated $87.4 billion, so that does put things in perspective. (I would love for my home to only make up 1.4 percent of my total net worth.)

On the flip side, there's Warren Buffett, who still lives in the home he bought in the 1950s for around $250,000 in today's dollars. Now it's worth approximately $650,000, which means it makes up .000007 percent of his net worth, which in simpler terms is less than 1 percent of 1 percent.)

Mark Zuckerberg paid $7 million for his home in Palo Alto, California, in 2011; that's .00005 of his net worth. Snap founder Evan Spiegel spent $12 million on his Los Angeles home; that makes up .001 percent of his net worth. (Compared with Buffett and Zuckerberg, Spiegel is clearly a spendthrift.)

You get the point.

According to Sarah Stanley Fallaw, author of the best-selling The Next Millionaire Next Door, the vast majority of the wealthy people she studied lived in homes that cost much less than they could "afford." 

And, in a broader sense, lived below their means -- which then allowed them to save, and invest, and build wealth over time. (Bitcoin millionaires aside, building substantial wealth typically takes decades.)

Which brings us back to that one question.

If you make money to spend money -- if spending money is more fun than making money -- then you will probably never get rich, at least in financial terms. 

If you borrow money that doesn't tend to generate a return, you will probably never get rich. With good credit and sufficient income, you can borrow $100,000 and buy a Porsche. If you have no credit and no income, you can borrow $200,000 to go to a private college and buy a degree.

Problem is, you eventually have to pay all that money back. Four years from now, your Porsche is no longer an "oh, my gosh, I own a Porsche!" It's just your car -- one you're still paying for. Ten years from now, if student loan payments are still a crippling financial burden, that investment in education may not feel so great. 

Sure you got a degree, but at what long-term cost? An education should be viewed as an investment -- one that generates a reasonable return.

As does any money you spend, whether personally or in business. Eventually, every business needs to generate a profit. Revenue needs to outweigh expenses. Otherwise, that business is just an expensive hobby.

That's why successful entrepreneurs, especially the ones who build thriving, long-term businesses, tend to operate well below their revenue means.

That's why wealthy people, or at least the ones that stay wealthy, tend to live below their income means.

And it's why billionaires enjoy making money more than they enjoy spending it.

As Frank Hasenfratz, the founder of Linamar, Canada's second-largest auto parts manufacturer, told Badziag, "There's one way to do it: Spend less than you make. If you spend less and you accumulate, you get rich."

Like most simple truths, spending less than you make, much less spending significantly less than you make, is an obvious strategy. But it can also be extremely difficult.

Unless you find a way to enjoy making money more than you enjoy spending money.

Because then your focus won't be on what you don't have.

Your focus will be on what you can do.