There is a truth that comes down to us from the ancient Greeks. We should pay attention to it, because it is one of the best reminders we have of how to lead well.

On an ancient Greek temple are chiseled the words, “Know Thyself.”

Now, there are many interpretations of these two words. Scholars will no doubt continue to argue about them for years. For our purposes here, though, let us just assume they mean what they say: You should know yourself.

In the work I do with leaders, often the most damaging barriers to stellar leadership and a productive firm are in the leader’s own personality. If he doesn’t know himself, if he doesn’t know the helpful and the dangerous in his own nature, he can be—quite literally— “the problem.”

Let me give some examples. Jed is the head of his firm and he is a fun guy. He loves people, he loves to celebrate, he is nearly always heading to or from food and wine. Life is wonderful. All the time.

Jed’s people love him, too. They want to work for him for the rest of their lives. It will all be a party. Yet the downside of Jed’s relational gifts is killing the firm. First, he is famously unclear. He likes people so much he just assumes that “they get it”—that they know what he wants them to achieve simply because he spends time with them. He never actually tells them what he wants, though. He just expects them to pick up his meaning by osmosis.

Jed’s second problem is that he is such a people person he cannot fire anyone. He can hardly move people around within the firm effectively. He doesn’t like change and he doesn’t like hurting people. He cannot make the changes necessary for success.

In short, Jed doesn’t know himself, so he can’t maximize his gifts and keep his destructive tendencies in check.

Here’s another example. Heather is a smart leader with a great resume and a history of certain kinds of success. She is a teaching machine. She leads by lecturing and for some in the firm this is perfect. Heather is clear, visionary, and knows how to make the firm produce.

Yet Heather, like Jed, is killing her company. First, the downside of her teacher gift is that she can seem arrogant, uncaring about the un-smart and the un-credentialed. This makes some of the most essential people feel small and unneeded.

Second, because Heather is so smart, she makes decisions alone in her office and then announces them to all as final decrees. There is no opportunity for a team to pitch in. There is no early buy-in. Decisions come down as though from on high. This creates resentment. It sends people looking for work elsewhere. It might make some employees respect Heather but it won’t make people love her and eager to fight battles at her side.

Jed and Heather need to know themselves. They need to take a close look at how they lead. They also need a team of trusted people around them who hold up a mirror, tell the truth, and bring other personalities and gift-mixes into play.

Both Jed and Heather can be brilliant leaders. They are simply leading in one or two dimensions now. If they work to know themselves and then work to round out their leadership styles with the help of others, they will cease being their own worst enemies in the great task of leadership.

You can do the same. Take a courageous look at yourself, enlist help, and then be better. Your best—and your worst—are within you. Extend the one and keep the other in check with the help of a good team. Great days are ahead for you.

That’s it. Have a good weekend.