Lewin’s Formula

An American soldier holds a flower behind his back. One of the first troops returning to Seattle from Vietnam.

By 1971, drug use by American soldiers in Vietnam was out of control. Not just weed. Lots of LSD. And lots of heroin. A 1971 Department of Defense report estimated that a third of American service members in Vietnam had tried heroin, and 1 out of every 5 was addicted.

Not good.

But something unexpected happened when heroin-addicted soldiers left Vietnam and returned to their homes in the US.

They quit.

You may have heard… heroin addictions are hard to shake. 80% of recovering addicts relapse within a year.

But among service members who became heroin addicts in Vietnam, only 5% relapsed within a year of returning home.

What happened?

One explanation is that it may have been easier for returning soldiers to quit because their behavior was linked to their old environment, Vietnam.

Kurt Lewin is the “founder of social psychology.” In 1936, he introduced a simple equation describing how our behavior is shaped by who we are and our surroundings.

B = f(P,E)

Where B is behavior, P is person, and E is environment. 

Lewin’s formula says behavior is a function of a person and his or her environment.

Writing this out as a formula almost feels silly because the idea seems like common sense. But that’s the beauty of it. It’s simple. And the implications of this insight are real.

P is the entirety of our person.  Our past, present, and expectations of the future. Our personality, strengths, limits, and motivations. 

E is every aspect of our environment. The roads we drive and bridges we cross. Our climate and colleagues. Our kids’ schools, our favorite lunch spot, and the conversations we overhear at the gym. And the availability and social acceptability of hard drugs.

The Vietnam War began in 1955. America sent ground troops in 1965. By 1971, one out of every five service members was addicted to heroin.

And when they came home, 95% of them successfully quit.

Their environment changed. And their behavior changed with it.

I’m not an addiction expert. Zero authority. But Dr. Lee Robins of Washington University in St. Louis is. And in 1977, he and some colleagues published Vietnam Veterans Three Years after Vietnam: How Our Study Changed Our View of Heroin.

Sometimes grit, determination, and willpower aren’t enough to change our behavior. There are some addictions and habits that can overpower the strongest willed among us.

When grit, determination, and willpower aren’t enough, we might consider another approach. Focus on the E instead of the P.

B = f(P,E)

In some cases, the real secret to changing our behavior might be changing our environment.