If I were to sit down at a coffee shop with leadership gurus John C. Maxwell, Ken Blanchard, and Simon Sinek--who have collectively sold a gazillion best-selling leadership books--and ask them this question, do you know what they would tell me?

Gentlemen, give me the bottom line, once and for all: What's the real reason people quit their managers, exactly?

I imagine Ken and John chuckling over their lattes before answering, as they've probably been asked this question an equal gazillion of times, since this is what they have written about over four decades. Sinek, the newer kid on the block, will probably give you that confident smirk under his spectacles, not say anything, and lift up a copy of Leaders Eat Last in his hand.

The No.1 Reason Employees Quit

After sipping their drinks and pausing to politely allow the others to chime in first, they would each reflect on the real reason people quit their managers.

Marcel, it's because the people charged with ensuring their success don't care enough to meet their needs as valued employees and human beings.

So there you have it.

And this is consistent with leading research by Gallup. In one study of 7,272 U.S. adults, it found that 50 percent of employees left their job "to get away from their manager to improve their overall life at some point in their career."

Gallup CEO Jim Clifton summarized this unfortunate phenomenon in a succinct sentence when he said this in the State of the American Workplace report:

The single biggest decision you make in your job--bigger than all the rest--is who you name manager. When you name the wrong person manager, nothing fixes that bad decision. Not compensation, not benefits--nothing.

Hard Fact: Employees Come Before Customers

And therein lies the problem for managers still operating in traditional hierarchies, which represents the majority to this day. They have it all backwards.

Blanchard is famous for teaching the concept of an "upside down pyramid," where leaders serve the employees, who are closest to the customer experience, first. He says:

Great leaders realize that their No. 1 customer is their people. If they take care of their people, train them, and empower them, those people will become fully engaged and gung-ho about what they do. In turn, they will reach out and take care of their second most important customer--the people who buy their products or services--and turn them into raving fans.

Case in point, in my most recent interview, profiling the CEO of The Melting Pot restaurant chain (who rose to the top from his lowly beginnings as a dishwasher), Bob Johnston revealed that the premise for the success behind his global fondue franchise comes down to an unwavering focus on "treating our employees well, so they'll treat our customers well." He adds, "If you ignore the first part of the equation, you'll never get to the second."

But first, employees need to feel like they belong, and trust, not fear, their leaders. This is about the emotional currency that leads to high performance.

In Sinek's Leaders Eat Last, he talks about the concept of the "circle of safety." The world is filled with danger, things that are trying to frustrate our lives, reduce our success, or reduce our opportunity for success. The only variables, says Sinek in this TED Talk, are the conditions inside the organization, and that's where leadership matters, because it's the leader who sets the tone to make sure there's trust and cooperation, and that employees' needs are being met.

He brings the point home: "When a leader makes the choice to put the safety and lives of the people inside the organization first, to sacrifice their comforts and sacrifice the tangible results, so that the people remain and feel safe and feel like they belong, remarkable things happen."

Bringing Leadership Back to Its Roots

Stripped down to its basic and most practical form, these leadership sages would agree with me that leadership has always been and will always be about meeting the needs of people and developing them to their fullest potential.

When employees don't get the tools, training, time, development, clear expectations, vision, or resources they need to do their jobs well, they experience low morale. They stop caring and they stop trying, unfortunately, early on in the game.

That's why Gallup put together these 12 crucial questions to help managers determine whether they are truly meeting the needs of their employees and ensuring their success.

When the rubber meets the road, the question that will define your leadership will always come down to, "Are you meeting the needs of your people?"