Approximately 30% of all the leaders we’ve studied have at least one fatal flaw. Everyone has weaknesses, but over the course of administering assessments to tens of thousands of leaders, we have found that most of the time that mild weaknesses do not impact a person’s overall effectiveness. Thus, while leaders usually aren’t aware of their weaknesses, this doesn’t hurt them.

Fatal flaws, however, are different. These are weaknesses that are so extreme that they can have a dramatic negative effect on a leader, seriously hampering their contribution to the organization and their career progress. Everyone else can see this clearly; but the person with the fatal flaw almost never does. And here, that blindness has a steep cost. Leaders don’t need to be extremely good at everything, but they generally cannot be totally void in one area and still succeed.

Why Weaknesses Are Hard to Self-Diagnose

Why are weaknesses and fatal flaws so hard for us to spot in ourselves? Here’s our theory. Strengths are seen as a direct outcome of some specific behavior exhibited by the leader. For example, they are extremely effective at solving problems and can point to specific instances where their quick thinking saved a project. Or they’re extremely good at marshaling their team to produce excellent work,  and have seen the impact in the form of happy clients or industry awards. The leaders recognize something they do that produces a positive reaction, followed by a positive business outcome.

Weaknesses — especially fatal flaws — are the opposite. Fatal flaws are “sins of omission.” They’re a result of inaction, of the leader not doing something. In our assessments, some of the fatal flaws we see most often are a lack of strategic thinking; not taking responsibility for outcomes; and not building strong relationships. We occasionally do find leaders whose fatal flaws are “sins of commission” — like a boss with a terrible temper, or an executive who lies — but those people are (fortunately) very rare.

Because most fatal flaws are sins of omission, they are harder for to see in ourselves. The result, after all, is not visible. It’s a deal that never happens, or a project that doesn’t exist. These leaders are simply not making things happen.

When they get their low scores back, these leaders often say to us, “But I’ve done nothing to deserve these ratings.”  However, we know their colleagues are thinking, “You deserve these ratings because you’ve done nothing.”

Becoming More Self-Aware

There are several ways you can learn to identify your weaknesses, and start to figure out whether they are serious or mild.

You can start by finding a “truth teller” who will share honest feedback with you.  Our data shows that a large number of colleagues know about or see firsthand a serious failing in their colleague. Such people just need to be found — and encouraged to speak.  They have to believe that you genuinely want honest information.  If they begin to convey the truth in a cautious, tentative way, encourage them to open up by being proactively receptive. Your reaction will allow you to hear the complete story.

If that doesn’t work, consider hiring outside help.  We wish we could tell you that you could simply think your way to greater self-awareness, but the truth is, that’s really hard to do. If your company doesn’t offer coaching or 360-degree feedback (we may be biased, but we do think it’s the best way to improve self-awareness), consider hiring a coach or therapist on your own. (Therapy is often covered by health insurance, while coaching is not.) This person may be able to help you gain a better understanding of your weaknesses and find ways to remedy them.

Think about it. If roughly one-third of leaders have a fatal flaw and you are sitting in a management meeting, look to your right and then to your left. As the old joke goes, if in your opinion, neither of these two colleagues has a really serious weakness, then the laws of statistics suggest that you do.