The people with power in any organization are usually its top performers. (Not always, I know, but that's a topic for another post). It's natural to assume that the reason they've ended up with so much power is precisely because they are top performers. But in many cases, it's the other way around--power creates peak performance.
Studies show that powerful people, even when working alone, work differently than those with less power. Often, their work is simply better. This is true regardless of how long the person in question has been powerful--in fact, you can bring people into a room, assign one of them at random to be the "leader," and immediately begin to see the difference.
Psychologists find that power leads to better performance, particularly on complex or difficult tasks that require effort and persistence, for four reasons:
1. Leaders feel responsible to the group they are leading, and to its goals. This is an added motivation that followers often lack.
2. All eyes are on them. Leaders feel more individually identified and therefore more accountable for their own work. Because they expect to be noticed by others, they feel pressured to set a good example.
3. Power stimulates the brain -- specifically, what psychologists refer to as the brain's executive function, which is instrumental when it comes to achieving goals. When participants in the laboratory are given power over the outcomes of others, we find that they are better able to control their attention, plan future behavior, and take goal-directed actions, all hallmarks of superior executive function.
4. Power keeps you going. A recent set of studies  show that powerful people not only outperform the less powerful, but that they continue to be able to do so even when their energy and willpower has been seriously depleted.
Self-control is a limited resource--like a muscle in your body, it gets tired when you've given it a good workout. Typically, when you've depleted your self-control by working on something really challenging, your performance on subsequent tasks suffers. Powerful people, however, are slower to show signs of depletion--they can keep up their A-game longer, thanks in part to their strong motivation and heightened executive functioning.
It's worth noting that powerful people don't always outperform the less powerful. After all, leaders have a lot on their plates--they can't possibly bring their best to everything. This raises the question of delegation. How do they (and should they) decide where to put their effort?
The short and unsurprising answer is that they generally withhold effort when the task in question is unworthy of a powerful person. In other words, when it seems like the kind of thing an underling would do. This attitude can and does affect performance. For example, in the studies I mentioned earlier, when the participants were given boring, repetitive tasks like filling out multiplication tables, those assigned to a leadership role performed worse than nonleaders, and complained that they didn't think it was the sort of task a leader should have to do.
Arrogant as this may seem at times, you have to admit that this attitude makes sense. Powerful people approach tasks with greater energy and intensity, but their well of energy and intensity isn't bottomless. They need to be selective.
Unfortunately, they don't always pull it off, which brings us to the serious weakness that comes with power. Making decisions about what is and isn't worthy of a leader's limited resources actually requires resources--when you are overworked, tired, or otherwise depleted, you have a hard time appraising a situation correctly.
Overworked leaders often don't realize that a particular task is really more appropriate for a subordinate to perform--they end up trying to bring their A-game to everything. They make bad choices, burn out, and their performance suffers.
So if you are fortunate enough to be given a position of power, it's quite possible that your best performances lie ahead of you. Even your brain is primed to rise to the challenge. But beware of the leader's Achilles heel--if you are too burned out to make good decisions about what to delegate, you'll end up squandering many of the performance advantages that your power has given you.
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