Author: Robert B. Kaiser and Robert E. Kaplan

At her funeral ceremony tomorrow, we will remember Margaret Thatcher as much for her leadership style as for her polarizing politics — in fact, the two are almost identical. The essence of Thatcher’s leadership was her steadfast, tenacious, and determined style which is more often associated with revolutionaries than conservatives. As the head of the Conservative party, she attacked the status quo and stuck to her guns in driving her agenda through opposition. It is precisely those qualities that made her the most influential British politician since Winston Churchill.

However, just as we’ve found in our decades of experience consulting to senior leaders — including CEO’s of major companies — Thatcher’s greatest strengths were also her biggest weaknesses.

Leadership is often defined in terms of opposites — autocratic vs. democratic, task-oriented vs. people-oriented, short-term vs. long-term. One fundamental duality — most evident in Prime Minister Thatcher’s case — concerns a leader’s interpersonal style: the assertive, forceful approach vs. a participative, enabling approach.

Most leaders intellectually understand the complementary nature of forceful and enabling leadership. Nonetheless, we find over and over again that few leaders are able to integrate both sets of behaviors in their own repertoire. Instead, they gravitate to one side or the other and risk taking that approach to such an extreme that it reduces the complementary approach to a void. We have all seen hard-charging, forceful leaders who come on too strong and diminish the ability of other people to contribute. And we have all seen the flipside, when a supportive people-person seems unable to make the tough calls and drive for results.

It’s a scary proposition for most leaders that the very qualities that have been central to their success can turn out to be the biggest threats to their careers, as we explain in Fear Your Strengths. This raises a choice every leader must make, even if most don’t give it much thought: Should you keep playing to your strength and risk overdoing it, or build up other capabilities where the odds of success are uncertain? Let’s take Thatcher’s story as a case study:

Margaret Thatcher was, as HBR senior editor David Champion put it, a fighter. It was her trademark grit, determination, ideological certainty, and scorn for consensus politics that drove her political achievements — privatization and the revitalization of the British economy, full repudiation of the socialist experiment, standing up to the tyranny of the Soviet Union. She gained so much respect on the world stage that Britain was able to exert great influence around the globe, winning over none other than U.S. President Ronald Reagan as a vocal advocate.

But it was overdoing those strengths that made Thatcher so divisive. She could be obstinate, stubborn, uncompromising; what The Economist called “a prim control freak.” Her fighting spirit left her with a cabinet that had learned its lesson too many a time: It was pointless to contradict or challenge her. She denied herself a loyal opposition — a counterforce to keep her honest, to challenge thinking, to test out ideas, and elevate understanding. Thatcher dealt with healthy opposition within her camp the same as she dealt with opposition from rivals: She came out swinging.

“I must say the adrenaline flows when they really come out fighting at me and I fight back,” she once said, “I stand there, and I say ‘Now come on Maggie, you are wholly on your own; no one can help you.’ And I love it.”

It was her unwillingness to consider other opinions and refusal to back down on what seemed a relatively minor domestic issue — a new system of local taxation called the poll tax — that led to her political downfall. Even when key cabinet ministers warned her that the measure would backfire, she fought on, crossing the line between conviction and rigidity. Shortly after, violent public protests erupted and her approval rating plummeted to 20 percent, the lowest in British history. By the end of the year, she was forced to step down. John Major, her successor, promptly eliminated the poll tax in favor of the council tax that still exists today.

Now, the straightforward advice for forceful leaders like Margaret Thatcher is that they have two options: They can ease up at times on their great ability to take strong stands and hold their ground — that is, choose their battles more selectively. They can also do the opposite of what they’re good at — allow a trusted advisor or group of advisors to influence them — to help keep their worst tendencies in check. Admittedly, for self-made types like Thatcher whose life experience has taught them that they can only count on themselves, that’s counterintuitive. Still, we’ve seen it done. Tigers can change their stripes, at least enough to stay out of trouble.

But here’s our question for you: What if Prime Minister Thatcher had learned to be more open to influence and selective in choosing her battles — could she still have had the tremendous impact that she undeniably had, but with a perhaps more graceful exit from office? Would her legacy have been remembered differently — more firm than rigid, more strong than stubborn, less polarizing and divisive?

Perhaps the biggest fad to sweep through management in the last decade was the strengths movement. Its message was that you should build on natural talent to maximize strengths rather than try to improve weaknesses. It was the brainchild of Donald Clifton, the late grandfather of Positive Psychology, but is associated in the popular culture with Marcus Buckingham, Clifton’s coauthor of Now, Discover Your Strengths (2001).

Like any successful movement, the strengths movement drove a single issue and inevitably left out a lot. Although several important things got overlooked, we want to call attention to a very real danger: Strengths can become weaknesses when overused.

Our new book, Fear Your Strengths (2013), is a cautionary tale based on 50 years of combined experience assessing thousands of leaders and coaching hundreds of executives. We’ve seen virtually every strength taken too far: confidence to the point of hubris, and humility to the point of diminishing oneself. We’ve seen vision drift into aimless dreaming, and focus narrow down to tunnel vision. Show us a strength and we’ll give you an example where its overuse has compromised performance and probably even derailed a career.

We’ve studied the extent of the problem with an innovative assessment tool, the Leadership Versatility Index. The tool uses the 360 method of gathering ratings from bosses, peers, and subordinates, but instead of the typical five-point rating scale that assumes “more is better” it has a unique scale that ranges from “too little” to “the right amount” to “too much.” Coworkers can therefore indicate if a manager overdoes it on four dimensions of behavior: forceful, enabling, strategic, and operational. Most executives are rated “too much” on at least one of these dimensions [PDF].

Further, the more pronounced your natural talent and the stronger your strengths, the graver the risk of taking them to counterproductive extremes. In one study, we compared coworker ratings on the Leadership Versatility Index to leaders’ strengths as identified by the Clifton StrengthsFinder, a questionnaire that managers fill out themselves to identify their natural talent. There was a clear correlation between having talent in certain areas and overdoing behaviors associated with those talents. For instance, leaders whose StrengthsFinder results indicated such talents as “Achiever,” “Activator,” or “Command” were more often rated as doing “too much” forceful leadership. Similarly, those who had the talents “Developer,” “Harmony,” or “Includer” were more often rated as doing “too much” enabling leadership. Overall, leaders were five times more likely to overdo behaviors related to their areas of natural talent than areas in which they were less gifted.

Taking these strengths too far has consequences. Across thousands of managers ranging from middle management to CEOs and spanning the US, Latin America, Europe, and Asia, we find a curvilinear relationship between leader behavior and employee engagement, team productivity, and effectiveness. In every case, these outcomes are lower for managers rated “too little” on the leader behaviors, peak for those rated “the right amount,” and drop back down for those rated “too much.” Overdoing it is just as ineffective as underdoing it.

One of the more counterintuitive things we have discovered is that not only do many leaders not know what their strengths are, but they also downplay and deflect feedback about their strengths. It takes extra effort to get the strengths to sink in, but doing so is prerequisite to fine-tuning how you use them. Fine-tuning is an art that requires an exquisite blend of both self-awareness and situational awareness.

Be aware of yourself. To handle the challenges that come your way, you must be able to read and respond adeptly. This requires knowing your default tendencies — for instance if you are more achievement-oriented and commanding, then you may be biased to respond too forcefully. Self-awareness allows you to respond mindfully to the needs before you, rather than out of habit. As one executive exclaimed upon making the connection, “I don’t have to give up my fastball; I just don’t have to throw it all the time!”

Be aware of the situation. We find it helpful for leaders to think of adjusting their strengths like a volume control [PDF]. The trick is to get the setting just right for the situation — from soft music for a quiet, intimate exchange, to a louder and lively level for a dance party. Knowing how much passion to put in a speech, how seriously to stress a concern, how long to let a discussion go on, how deep to get into the details, how fast to drive a change initiative — all of this requires a deft touch, equal parts knowing your own strength and knowing your audience.

It is neglectful if not irresponsible to emphasize strengths without warning leaders that the stronger the strength, the greater the danger of taking it too far. Toning down overused strengths requires a different approach from the skill development needed to improve upon a weakness, where the challenge is adding to a repertoire with basic skill building. Getting a strength under control is about refining a skill you already have. It requires learning to be more selective about what situations call for that strength and calibrating how much is enough, versus too much.