The study: Harvard’s Maryam Kouchaki and a colleague, Isaac H. Smith of the University of Utah, enlisted participants for what was ostensibly a decision-making experiment but was really a study of dishonest behavior. If subjects lied, they could earn more money. People’s tendency to be untruthful was greater in the afternoon than in the morning, the researchers found. They attributed this result to the “psychological depletion” people experience as a day wears on, which makes them cognitively weaker.

The challenge: Could the stresses of an ordinary day really turn us all into liars after lunch? Should companies be extra vigilant about unethical behavior in the afternoon? Dr. Kouchaki, defend your research.

Kouchaki: We replicated the finding in four experiments. It was clear: People were 20% to 50% more likely to be dishonest in the afternoon—we chose 3 to 6 PM for our afternoon sessions—because they were depleted of the resources they needed for self-control. Gradually increasing fatigue from unremarkable activities can lead to systemic moral failure. Even ethical people can’t avoid it. In fact, the effect was strongest for people with a lower propensity for moral disengagement. That is, people who usually behave more ethically were the most susceptible to the negative consequences.

HBR: It’s hard to believe that a day of meetings, phone calls, and other office work would be so tiring that it would push an employee into making an unethical choice.

People certainly have good days and bad days, and good days aren’t very depleting. In fact, they can be energizing. If someone says your efforts are really appreciated or you successfully conclude a contract, you might feel so good that you suffer no cognitive depletion in the afternoon. But we looked at averages. On average, people tend to get tired out by the stresses and strains of the day. And a lot of people’s days, in the current business climate, are very stressful.

Timing Counts Average percentage of study participants who lied to obtain small monetary gains

Does that mean project managers shouldn’t be allowed to fill out progress reports in the afternoon? That accountants should be kept away from the books?

It’s important to be practical. I wouldn’t advise companies to establish burdensome rules, but they should take deliberate action to avoid systemic pitfalls, and there are simple ways to limit opportunities for immorality. For example, tasks with a moral component can be shifted to the morning and after breaks, when managers and employees are less depleted. At the very least, try to avoid scheduling those activities at the end of the day.

I still have trouble accepting that people are less depleted in the morning. If you gave me a moral choice before I’ve had my coffee, there’s no telling what I might do.

Of course, there are individual variations. “Morning people” tend to be more alert in the AM, and “evening people” perk up late in the day. You may be right—you may make your best moral choices after you’ve had your coffee, after lunch, or even late at night. But again, we’re talking about averages.

If being depleted makes us revert to unethical behavior, doesn’t that imply that humans are naturally unethical? Is everyone really corruptible given the right circumstances?

There is debate over that question in psychology. Some studies have shown that people default to their own self-interest; others show that they default to cooperative—in other words, ethical—behavior. What matters is that when self-interest conflicts with the motivation to be ethical, a person usually requires self-control in order to stick with the moral behavior. And when you’ve been thrown for a loop by your manager’s criticism, a customer’s complaint, or a call from the car dealership saying that replacing your side mirror is going to cost $900, you may not have the mental resources to maintain your self-control. That applies especially to people who are generally the most morally engaged—people who pride themselves on doing the right thing.

But wouldn’t the most moral people have the strongest motivation to behave ethically? Doesn’t motivation count for something?

Yes, it does, and I agree that the finding about the effect on people who are the most morally engaged is counterintuitive. But the way to look at it is not so much that highly moral people are overly depleted by the day’s activities, or that they are less motivated to be ethical, but that people who are low in moral engagement are less affected by depletion simply because they don’t have much morality to lose. They are less likely to draw on self-regulatory resources to begin with.

So after a long, trying day, moral people become like their immoral colleagues.

Sort of. I should point out that in corporations, ethics or the lack thereof extends way beyond the obvious transgressions such as cooking the books, embezzling, and lying about credentials. Most jobs have an ethical component. You’d be hard-pressed to think of one that didn’t. There are many situations in which we must make small moral choices. Should I leave that mess for someone else to clean up? Should I write my report in such a way as to make my coworker appear less competent than she really is? Should I conceal my own incompetence? And so on up the ladder of ethical magnitude. By the way, when your psychological resources are depleted, you’re less likely to even recognize that an intended action (or inaction) has moral implications.

Maybe we should all stop working after 3 PM.

In some cultures, afternoon breaks or siestas are an accepted part of the business day. In the West people tend to take a dim view of them, but breaks can serve the valuable purpose of restoring our depleted energy, positioning us to make better choices. Self-control is like a muscle—we need to restore its strength after use. Rest, relaxation, meditation, prayer, a snack—all those things can help restore us.

Or maybe we should just stop working so hard.

People do work hard. People I know in financial services and in Silicon Valley have told me how exhausted they are by the end of the day. Some even take pride in maintaining an almost nonstop intensity over the course of long days. They feel that working brutal hours is part of fulfilling the company’s mission. That’s fine, but they should know that factors beyond our control can influence our behavior. Exhaustion has costs, and one is a loss of control over the ability to make ethical choices. Are you really fulfilling your company’s mission if you can’t maintain your moral bearings?

Interview by Andrew O’Connell