The Peak-End Rule

There’s a cognitive memory bias called the “Peak-End Rule”–––given any experience, our memory of it will focus on the peak, or most intense moment(s) and its end.

Behavioral scientists have conducted all sorts of bizarre experiments to prove this intuitive rule. For example, one set of volunteers is asked to plunge their hands into freezing water for a few minutes. Another set is asked to endure the same uncomfortable temperature for the same uncomfortable time, but then an extra minute of plunging is added at the end at a less frigid temperature. It’s the second set of volunteers who will report that their experience was less unpleasant, despite enduring more aggregate discomfort time. There’s a similar version having to do with colonoscopies, but I’ll spare you.

What’s most interesting to me about this rule is its converse. If in retrospect we overvalue certain elements of our experiences, it must mean that we undervalue other elements, namely the much more frequent non-peak moments and all the moments that come before the end. And the “end” could be replaced by “the most recent” if the experience is not yet over.

I think the peak-end bias can be applied to experiences with varying lengths of time, from a few minute cold plunge to a restaurant meal to a vacation to a long relationship to an entire lifetime. (Selfish suggestion to restaurants: end my meal with a few delicious petit fours and I’ll forgive any prior lapses in food or service).

My cognitive weapon of choice to battle the peak-end rule is perspective, meaning that we need to use our mental capacities to take a lofty enough view so that we can see the entirety of the experience, not just the peaks and the end/most recent stage. That doesn’t happen naturally; it takes effort.

Most importantly, all long and vibrant relationships require this perspective. Your desire to be with a friend, a sibling, a child, or a spouse, will inevitably have moments or periods of dissatisfaction and disengagement due to hurt feelings or disappointment or any of a thousand reasons.

How self-defeating would it be to judge a successful multi-decade marriage or friendship by a relatively small fraction of its tenure that happens to be both recent and poignantly disagreeable? I wonder how many relationships suffer such an unnecessary end, precisely because we fail to fight against the natural inclination of the peak-end rule. We fail to take an historical perspective, and in failing to do so, we risk losing something of inestimable value. Something we might never be able to retrieve or replace.

Of course, there are certain actions that are so disagreeable as to fatally ruin a relationship. A betrayal severe enough to alter fundamentally and permanently how we see the other person. But I think that’s rare. More common would be a drift due to changed circumstances. Or a drift caused by a misunderstanding or a breach of etiquette like an unexplained failure to attend an important event. Such a drift, if left uncorrected, can and will become accentuated, like a satellite that veers slightly from its orbit and, left to its own devices, will find the error of its trajectory increasing with each revolution until it eventually escapes the pull of gravity and disappears into space, lost forever.

But let’s take a different sort of experience that’s enjoying a recent and long stretch of great success. And what if the intensity of a negative peak event is far enough in the past that we never experienced it for ourselves. Or even if we did, it’s old enough to have lost its potency, made dim by time.

Now we enter the realm of history. And I’m thinking specifically about financial history. I’m old enough to have been working in finance when the dot-com bubble of 1999-2000 burst and during the great financial crisis of 2008-2009 (neither of which I saw coming.) But what if you didn’t experience either? Or even if you did, you think of these events as belonging to another era, as relevant to you as the French Revolution or the Peace of Westphalia or whatever killed the dinosaurs.

Then you cannot conceive of the stock market going down 50% as it did during those two periods of time. It’s completely contrary to anything that you hold in your memory. And that’s another danger of the peak-end rule. The “end” or most recent stage, in this case fifteen years of financial plenty, may have persisted for so long that it becomes to seem eternal. As if it will go on forever.

I’m a skeptical and conservative investor, but if you ask me if it’s possible for the stock market to decline 50%, my emotional instinct, rather than my intellect, is to reply ”absolutely not!” My instinct tends toward the complacent just as the rule dictates. I feel the same way about Russia using tactical nuclear weapons. No nuclear weapon has been used as a weapon of war since Hiroshima and Nagasaki, 80 years ago. So my instinct says that it won’t happen, that it can’t happen. My brain says otherwise.

Studying history is a way to combat complacency. What has happened before can happen again.

Circling back to relationships, I’ve lost a sibling to a family rift. I suspect most families have similar stories to tell. Recalling this loss is painful but instructive. It fights against my instinct that all my relationships, fine now, will forever stay that way regardless of circumstances. That’s a complacency I want to combat. Even if I have to contemplate history that’s unpleasant and stressful.

Doing so reminds me that I don’t ever want to lose a close relationship through inaction or carelessness on my part. It makes me aware that if something goes a little off course, best to correct it as soon as possible.

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