Editor’s note: James Forr is director at Olson Zaltman Associates, a global market research firm based in Pittsburgh, Pennsylvania. This is an edited version of a post that originally appeared here under the title, “The dangers of data.”

Shortly after taking office, John F. Kennedy’s rough-and-tumble Vice President Lyndon Johnson visited his old Texas mentor Sam Rayburn, the former speaker of the house, to gush about all the wonderful things the cabinet and staff glittered with Ivy League degrees and exalted pedigrees – such as then Secretary of Defense Robert McNamara – would do for the country.

Big data“They may be just as intelligent as you say,” Rayburn replied. “But I’d feel a helluva lot better if just one of them had ever run for sheriff.”

While McNamara never ran for sheriff, he earned his degree in economics from Berkeley and his MBA from Harvard, became assistant professor at Harvard at age 24 and then displayed his remarkable talent for statistical analysis in the Army Air Corps during World War II. He went to work at Ford where, among other achievements, he started up a market research division.

McNamara embraced big data long before the term existed and he brought this mindset to the Pentagon – specifically to the escalating tensions in Vietnam. As Kenneth Cukier and Viktor Mayer-Schonberger write in MIT Technology Review:

“Only by applying statistical rigor, he believed, could decision makers understand a complex situation and make the right choices. The world in his view was a mass of unruly information that  if delineated, denoted, demarcated and quantified  could be tamed by human hand and fall under human will. McNamara sought truth, and that truth could be found in data.”

This coldly rational way of looking at the world has gained increasing currency in market research circles – and elsewhere – in recent years as technology has put ever more data at our beck and call. Marketers have access to information about practically anything they want to know about consumers – click-through rates, browsing behavior, social media interactions, spending patterns, etc.

All of this information is extremely valuable. However, data is not meaning. Data does not equal understanding. For a marketer, knowing what people do is only half the equation. The other side of the equation is understanding why they do what they do. Insights into how people feel – about a product or service, about an experience or about their lives – are central to building a strong a brand.

For all of McNamara’s brilliance, he lacked wisdom and perspective. In Vietnam, he and others on the foreign policy side of the administration almost went out of their way to avoid deep insight. Advisors who had spent years in Southeast Asia and had an intuitive grasp of the history and culture were shunted aside, largely because of McNamara’s reluctance to give credence to viewpoints different from his own.

In place of wisdom came numbers: body counts, ships intercepted, bombs dropped, land controlled. By any statistical reckoning, the U.S. won the Vietnam War. In reality of course, the U.S. lost – and 58,000 Americans died in the process.

Armed with only data and not meaning, McNamara never could understand why our allies, the South Vietnamese, wouldn’t fight as hard as the Americans. He never could understand why the North Vietnamese didn’t waver, no matter how many bombs were dropped or how many of their soldiers died. (As the Vietnamese Foreign Minister told McNamara years later, “Don’t you understand that we have been fighting the Chinese for 1,000 years? We were fighting for our independence. And we would fight to the last man. And we were determined to do so. And no amount of bombing, no amount of U.S. pressure, would ever have stopped us.”)

McNamara also deeply misunderstood (or just ignored) how the collective emotions of the American people would impact the war effort. When CBS Evening News anchor Walter Cronkite publicly declared the war a lost cause in 1968, then-President Johnson reportedly said, “If I’ve lost Cronkite, I’ve lost Middle America.” No amount of number crunching could have anticipated that.

Forbes contributor Jonathan Salem Baskin has described several lessons that marketers can take from McNamara’s big data blunders but perhaps the most important one is that some things are impossible to quantify. Indeed, often the most important things in life are impossible to quantify. Do you love your spouse? Do you love your children? Fine – quantify it. In the minds of people like McNamara, if you can’t put a number on it, it can’t be true.

McNamara came to regret his role in the war but it isn’t clear he fully learned the lesson. He left the administration and became president of the World Bank in 1968. His tenure there wasn’t particularly successful, either. His belief that the bank could alleviate poverty in the developing world simply by pouring money into rural areas proved to be a fallacy – again, because he blinded himself to the political and human factors at work in those nations. His legacy at the World Bank also suffered because he ignored burgeoning global environmental concerns – he did so largely because those concerns could not be quantified.

Later in life McNamara stated, “I try to separate human emotions from the larger issues of human welfare.” This is where he went wrong. One cannot hope to solve the larger issues of human welfare without understanding the role of human emotions.

We are not making decisions on the scale of Robert McNamara. No one is going to die if our pet food isn’t properly positioned or if that new laundry detergent campaign doesn’t work. Nonetheless, his career in public service is an object lesson in the hubris of numbers. Big data is a wonderful tool but without big understanding it is nothing.