If you're a good leader, you know you should praise your employees. If you're a good leader, you know you should provide useful, timely feedback. If you're a good leader you know, in general terms, what you should and should not say.

But if you want to be a great leader, and build a great team, you'll need to say these four words as often as necessary. While doing so will make you feel vulnerable... that's actually how you want to feel.

But what you may not know is how powerful an impact four simple words, spoken with the right intent, can have on others -- and on you and your business. Granted, they might make you feel a little vulnerable... but that's exactly how you should want to feel.

The following is from Daniel Coyle, author of The Talent Code (one of my all-time favorite books; I've given at least 50 copies to people over the years) and the upcoming The Culture Code: The Secrets of Highly Successful Groups (Jan. 30, 2018). Daniel went inside incredibly successful organizations like Pixar, SEAL Team Six, and the San Antonio Spurs to uncover three key skills that explain how diverse groups learn to function with a single mind.

I read an advance copy. It's great. Pre-order it. You'll be glad you did. I promise.

Here's Daniel:

When you think about great leadership, you tend to think about big moments: Daring decisions and inspiring speeches; moments when a great leader shows the path forward.

But in my research, I kept seeing leaders deliver something different. They weren't big moments, but rather little moments of confession, when they admitted to a mistake or a weakness.

Dave Cooper, a Navy SEAL, put it this way: "The most important words a leader can say is, 'I screwed that up.'"

At first, that seems strange. Shouldn't leaders project unshakable confidence? Doesn't admitting weakness risk creating more weakness? But when you look more closely, those words make deep sense. Because strong culture can only happen when its members feel safe enough to tell each other the truth.

That starts with moments when the leaders show their fallibility.

There's a name for this moment. It's called a vulnerability loop, and it works like this: Person #1 is vulnerable, and admits a mistake or a shortcoming. This allows Person #2 to do the same, creating high-candor exchanges that drive performance and build trust.

Vulnerability loops determine whether a group is going to be about merely appearing strong, or about actually facing hard truths and learning together.

Vulnerability loops are most powerful in moments of stress -- when something's gone wrong, or when there's a disagreement. "At those moments, people either dig in and become defensive, and start justifying, and a lot of tension gets created," says Jeff Polzer, a Harvard business school professor who studies organizational behavior. "Or they say something like, 'Hey, that's interesting. I'm curious and want to talk about it some more.' What happens in that moment helps set the pattern for everything that follows."

For example, here's Ed Catmull, president and co-founder of Pixar. The first time we met Catmull showed me around Pixar's relatively new studio building, named Brooklyn. It is a sunlit box of glass and reclaimed wood, brimming with insanely cool touches like a speakeasy, a fireplace, a full-service café, and a roof deck. As we walked, I made an offhand remark -- something like, "Wow, this building is amazing."

Catmull stopped and turned to face me. "In fact, this building was a mistake."

I leaned in, unsure I'd heard correctly.

"The reason it's a mistake," Catmull continued, "is that it doesn't create the kinds of interactions we need to create. We should have made the hallways wider. We should have made the café bigger, to draw more people. We should have put the offices around the edges to create more shared space in the center. So it wasn't like there was one mistake. There were really a lot of mistakes, along of course with the bigger mistake: That we didn't see most of the mistakes until it was too late."

And here is Cooper, the SEALs master chief who trained the team that captured Osama bin Laden. Cooper constantly went out of his way to show his fallibility to his team, to admit error. A new team member who called him by his title was quickly corrected: "You can call me Coop, Dave, or F*ckface, it's your choice."

When Cooper gave his opinion, he always attached phrases that provided a platform for someone to question him, like "Now let's see if someone can poke holes in this" or "Tell me what's wrong with this idea." He steered away from giving orders and instead asked a lot of questions. Anybody have any ideas?

During missions, Cooper sought opportunities to spotlight the need for his men to speak up, especially with newer team members. He was not subtle. "For example, when you're in an urban environment, windows are bad," he tells me. "You stand in front of one, and you can get shot by a sniper and never know where it came from. So if you're a new guy and you see me standing in front of a window in Fallujah, what are you going to say? Are you going to tell me to move my ass, or are you going to stand there quietly and let me get shot? When I ask new guys that question, they say, 'I'll tell you to move.'

So I tell them, 'Well, that's exactly how you should conduct yourself all the time around here, with every single decision.'"

By using vulnerability loops, Catmull, Cooper, and the other leaders send a crystal-clear message: We are about learning together. They give everyone in the group permission to tell the truth, thus generating high-candor exchanges that drive improvement and create a shared mental model on how to perform together.

They shift the focus away from self-protective instincts, and toward the truly important questions: What's really happening here?

How can we get better together?