I’ve been a leadership coach for over twenty-five years, and by far the most common question I get is: “What’s the most important quality in a successful leader?” People usually expect answers like, “confidence,” “innovative,” “fearlessness,” “vision,” and so forth. Don’t get me wrong, these are valuable qualities. But they’re not the most important. Not by a long shot.

The answer is humility.

The unfortunate truth is that most leaders aren’t humble. In fact, most people aren’t. A few years ago, researchers from Pepperdine University thought to calculate just how common humility was in the general population. They asked hundreds of participants to respond to statements like, “Others have more to learn from me than I have to learn from them,” and “My ideas are usually better than other people’s ideas.”

In the end, barely 10 percent of people scored highly on the test. In other words, science suggests that around 90 percent of the population isn’t humble. So, it makes perfect sense that most leaders aren’t either. We simply aren’t wired that way. But with hard work, we can learn to be humble. It takes a ton of practice. Otherwise, if you give the average person career success, wealth, positional authority, a corner office, stock options, and fame, there’s a 90 percent chance they become an arrogant leader.

That’s right, 90 percent.

Do you remember your first cell phone? If you’re of a certain age, it was probably a Nokia with plastic buttons and an antenna. (Remember when phones had buttons?) By the mid-2000s, Nokia was on top of the world. It commanded 50 percent of the smartphone market share. All its competitors were in the rear-view mirror and fading fast. However, it later came to light that many of Nokia’s top executives were feared by their subordinates. They regularly shouted at and belittled employees and threatened to fire or demote anyone who questioned their judgment. Then, in 2007, a guy named Steve Jobs unveiled the iPhone. And, well, you know the rest. Within six years, Nokia had lost 90 percent of its value.

That’s right, 90 percent. Poetic, isn’t it?

Nokia went the way of Kodak, Circuit City and Blockbuster because its leaders were arrogant. Now, I’m not saying that 90 percent of leaders are bad people. They might have plenty of great qualities. Arrogant leaders may not always scream at their employees, but maybe they don’t listen to new ideas. Maybe they don’t take responsibility for their team’s mistakes. Maybe they don’t put the needs of their followers first.

I’ve been blessed to know a few leaders in the other 10 percent, including mentors like Walt Rakowich and Tim Stojka. Walt became CEO of a global real estate company after its market capitalization dropped from $20 billion to less than $500 million during the Great Recession; he then engineered one of the greatest corporate comebacks in Wall Street history. Tim, meanwhile, is the CEO of an extraordinarily successful software and data analytics firm. The three of us had dinner recently with a handful of bigshots, including an executive from Ritz Carlton and the heads of the biggest country clubs in southwest Florida. When you’re in a room with powerful people like that, your impulse might be to brag about your accomplishments. To prove you belong at the table. We went around the table introducing ourselves, and when we got to Walt, he only talked about the teenagers he’s mentoring through the nonprofit Colorado UpLift. When we got to Tim, he briefly mentioned how honored he was to speak to a few students at a school near his home. I later found out that Tim had actually delivered the commencement address to Northwestern University’s engineering school.

People like Walt and Tim weren’t born this humble. They worked hard to earn loyalty from their employees. They sought out the smartest men and women in the room and learned from them. They still do. They admit when they make mistakes. They focus on developing others before themselves. They follow the advice of C.S. Lewis, who once said, “Humility is not thinking less of yourself, but thinking of yourself less.”

You probably know some of these humble leaders in the 10 percent club. Most of them aren’t powerful CEOs. The biggest influence on my early life was my high school marketing teacher Deanne Singer, who made it her mission to help me believe in myself. The biggest influence on my adult life was my life insurance agent, Jerry Middel, who has never stopped investing in me. He co-signed the mortgage on my first home, and we’ve had breakfast nearly every week for the past two decades. It was Jerry who taught me, “Keep your mouth shut and let other people brag about your accomplishments.”

Deanne and Jerry are in the 10 percent club. Walt and Tim are, too. I learn by their example, and I pray that I can become half as humble as them. Great leaders are humble. Great people are humble. But if you want to have tremendous influence on the lives of others—if you want to do what the 10 percent club does so well—speak and think less of yourself, and let other people brag about your accomplishments.