How predictable are humans?

Are humans more like clouds or clocks? In a world awash with data, it's easier to answer that question than ever before, but the results might surprise you.

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How predictable are humans? It’s not a straightforward question. We’re creatures of habit, but we’re also constantly being blindsided by major social changes as well as upheavals in our own lives. So, in principle, are we predictable?

It’s time for a few puzzles, to help explain why what’s most predictable is often the least important.

Consider these four charts below. See if you can figure out what they show, without any labels. (Don’t worry, there are hints). Charts 1 through 3 come from Google Trends. They measure web search frequency in the United States across time. Try to guess which word or phrase has created these data patterns, based on your assumptions about the regularity of human behavior.

Chart 1:

The search term in Chart 1 peaks every year around January 1st. However, it also peaked in April/May of 2020 and the peak around January 1st in 2021 was particularly high. What search term fits that pattern?

Chart 2:

Chart 2 shows a search term that steadily grew in popularity from 2009 to 2016, before becoming of slightly less interest. Each peak happens around September/October each year, then falls abruptly.

Chart 3:

The search term in Chart 3 peaks every year in the summer months. But there is one outlier: an enormous peak in the spring of 2007. Hint: the term is related to the weather.

Chart 4:

Chart 4 isn’t related to web searches, but does show a pattern of how some humans interact with one another based on the calendar year. Try to guess what it’s showing. Hint: the lowest data point in the year is Christmas Day; the highest data point is two weeks before Christmas; there’s a big increase in the spring; and there are small spikes every Monday.

I’ll reveal the answers in a moment, but what’s striking about all four of these charts is that they’re certainly not random. There is clear order. Chart 1, for example, is so repeatable (until 2020 at least) that it looks a bit like a heartbeat. The peaks in Chart 2 rise and fall, but there’s nothing erratic about it.

These patterns create a paradox. Our behavior and our societies do follow patterns. In aggregate, groups of humans can be highly predictable. We know, for example, that we’re more likely to get a table at a restaurant at 5pm on a Tuesday than 7pm on a Saturday and that assumption rarely turns out to be wrong.

And yet, our individual lives are not predictable. When we look back on the events that have shaped us, or examine the moments that rerouted our life paths, they are often highly irregular and sometimes even feel random. Most spouses can pinpoint a small deviation in the past that, had it happened, would’ve derailed the relationship in its early stages or caused the couple to never meet in the first place. Everything that followed may have pivoted on that little detail. Few of us can claim that our lives have turned out exactly as we expected.

Similarly, at the societal level, we’re terrible at predicting large scale change. We try, but frequently fail, to predict recessions and revolutions, election winners and pandemics. Even on more basic questions, we’re often wildly wrong.

Consider, for example, our intuitions about how society’s tastes and preferences shift over time.

Entire industries of seasoned professionals work to tackle those questions, from marketing to publishing. Yet, when one author pitched a new fantasy book series to publishers, she faced twelve rejections. “Children just aren’t interested in witches and wizards anymore,” one remarked. Finally, an editor decided to take a hesitant gamble, shelling out the paltry sum of £2,500 ($3,000) on the advice of his eight-year-old daughter, who was gripped from the first page.

Harry Potter went on to sell 500 million copies, making it the best-selling book series in human history.

Sometimes, we’re predictable. Other times, we’re not. How can we make sense of ourselves in a world defined by such contrasts? And what are those mystery charts?

In 1965, the philosopher Karl Popper addressed human predictability in a lecture he titled “Of Clouds and Clocks.” He suggested that it might be useful to try to divide the world into two pure types of behavior. On the right side of Popper’s spectrum are the clocks. These are systems or individuals that are neat and orderly, ticking away with extreme predictability. On the left side are the clouds. These are disordered, unpredictable, and erratic. Whereas Popper’s clocks follow rules, clouds follow nothing.

Popper places the movements of planets in our solar system furthest to the right, as we always know when Mars will rise on the horizon and we can predict the arrival of Halley’s comet with extraordinary accuracy. The changing seasons would be mostly to the right, but perhaps not as far to the right side as the orbit of the planets. On the left would be, say, a cloud of gnats that dart to and fro in frantic, unexpected ways. But, as Popper points out, such simple categories are insufficient. Individuals could be ranked differently within categories. An energetic puppy, he explains, is more cloud-like than an old dog that hasn’t learned any new tricks for some time and has little interest in barking at falling leaves or passing cars.