Take a moment to think about who you are right now.

Think about your closest relationships, your job, your geographic location, your current life circumstances. What would you consider your most indelible life experiences—the ones that have made you who you are? What are your most deeply held beliefs? What choices, large and small, good and bad, have led you to this place, to this moment in time?

These choices are routinely influenced, and sometimes completely determined, by memory. To paraphrase Nobel-winning psychologist Danny Kahneman, your “experiencing self” does the living, but your “remembering self”1 makes the choices. Sometimes these choices are small and mundane, such as what to eat for lunch or which brand of laundry detergent you grab from a crowded supermarket shelf. Other times, they are the driving force behind life-changing decisions, from what career to pursue and where to live to what causes you believe in, even how you raise your children and what sort of people you want around you. And further, memory shapes the way you feel about those choices. Kahneman and others have shown in many studies that the happiness and satisfaction you gain from the outcomes of your decisions do not come from what you experienced, but rather from what you remember.

In short, your remembering self is constantly—and profoundly—shaping your present and your future, by influencing just about every decision you make. That’s not necessarily a bad thing, but it does mean we need to understand the remembering self, and the mechanisms of its far-reaching influence.

Yet the pervasive involvement of memory in our thoughts, actions, emotions, and decisions often passes unnoticed, except for those moments when it fails us. I know this because, whenever I meet someone new and they discover I study memory for a living, the most common question I get is, “Why am I so forgetful?” I often ask myself the same question. Daily, I forget names, faces, conversations, even what I’m supposed to be doing at any given moment. We all wring our hands over those moments that we can’t remember, and as we get older, forgetting can be downright scary.

Severe memory loss is undoubtedly debilitating, but our most typical complaints and worries around everyday forgetting are largely driven by deeply rooted misconceptions. Contrary to popular belief, the most important message to come from the science of memory is not that you can or even should remember more. The problem isn’t your memory, it’s that we have the wrong expectations for what memory is for in the first place.

We are not supposed to remember everything from our past. The mechanisms of memory were not cobbled together to help us remember the name of that guy we met at that thing. To quote British psychologist Sir Frederic Bartlett, one of the most important figures in the history of memory research, “literal recall is extraordinarily unimportant.”2

So instead of asking “Why do we forget?” we should really be asking, “Why do we remember?”

My first step toward answering this question began on a windy fall afternoon in 1993. I was a twenty-two-year-old graduate student working on my PhD in clinical psychology at Northwestern University, and I had just designed my first research study on memory—although it wasn’t supposed to be about memory. I was doing research on clinical depression, and we designed the study to test a theory of how being in a sad mood affects attention. I walked into Cresap Laboratory with a song by Hüsker Du (whose band name is Norwegian for “Do you remember?”) blasting in my headphones to psych myself up as I prepared to collect electroencephalography (aka EEG) from my first subject. I found myself struggling to attach electrodes to the scalp of a college student with a head of thick curls. After thirty minutes of staring at the computer monitor, mesmerized by the waves of electrical activity emanating from her brain, it was time to remove the electrodes and clean up. Despite my best efforts, when she left the lab, her hair was spackled with a crust of thick conductive paste.

The idea was to make otherwise emotionally healthy subjects feel sad and then observe whether being in a sad mood led their attention to be captured by negative words (such as trauma or misery) more than neutral words (such as banana or door). To get our volunteers into a sad mood, we had them listen to a selection of slowed-down classical music, including “Russia Under the Mongolian Yoke,”3 by Sergei Prokofiev, from the film Alexander Nevsky—a song so effective at inducing sadness it’s been used in a number of studies on clinical depression. While the music played in the background, we asked our volunteers to reflect on a past event or time in their lives when they were sad. We expected that the music would make it easier to remember a sad event, and that remembering a sad event would make people feel sad. We were correct. Worked every time.

The rest of the experiment was a bust, but what stuck with me was that we were able to use people’s memories of the past to change how they felt and looked at things in the present. It wasn’t just that thinking about a painful event in their past made them sad; it seemed that being sad made it easier for them to remember other sad events. From that moment on, I became fascinated with how the structures of the brain that give rise to what we think of as “remembering” can profoundly affect how we think and feel in the present moment, and thus how we move into the future.

Memories can be triggered in a lab by a mournful piece of classical music, but in the real world they often sneak up on us at the most unexpected times and from the most unlikely sources—a word, a face, a certain smell or taste. For me, it only takes two chords from “Born in the U.S.A.” to bring back a flood of memories about the people in junior high who regularly subjected me to all sorts of racist epithets.

The sounds, smells, and sights we experience in the present can also transport us back to joyful times. A song by the indie rock band fIREHOSE always takes me back to my first date with my future wife, Nicole; the smell of jackfruit reminds me of a walk on the beach with my grandfather in Madras, India; and the sight of the brightly colored mural outside a small Berkeley pub called the Starry Plough will send me back to my college days, when I played a memorable show with my college rock band, Plug-In Drug. (Yes, I regret that band name.)

Each of these remembered experiences and the feelings they elicit speak to one of the core principles that has underpinned much of my work, both as a clinical psychologist and a neuroscientist: Memory is much, much more than an archive of the past; it is the prism through which we see ourselves, others, and the world. It’s the connective tissue underlying what we say, think, and do. My own career choices were, no doubt, influenced by my experiences as a first-generation immigrant that left me with a lasting sense of “otherness.” So much so, I sometimes feel like an alien, probing human brains to try to figure out how and why people behave the way they do.

To fully appreciate the weird and wonderful ways in which the human brain captures the past, we need to ask the deeper questions of why and how memory shapes our lives. The various mechanisms that contribute to memory have evolved to meet the challenges of survival. Our ancestors needed to prioritize information that could help them prepare for the future. They had to remember which berries were poisonous, which people were most likely to help or betray them, which place had a soft evening breeze or fresh drinking water, and which river was infested with crocodiles. These memories helped them stay alive for their next meal.

Viewed through this lens, it is apparent that what we often see as the flaws of memory are also its features. We forget because we need to prioritize what is important so we can rapidly deploy that information when we need it. Our memories are malleable and sometimes inaccurate because our brains were designed to navigate a world that is constantly changing: A place that was once a prime foraging site might now be a barren wasteland. A person we once trusted might turn out to pose a threat. Human memory needed to be flexible and to adapt to context more than it needed to be static and photographically accurate.4

This is therefore not a book about “how to remember everything.” Rather, in the chapters to come, I will take you into the depths of your memory processes so you can understand how your remembering self can influence your relationships, choices, and identity, as well as the social world you inhabit. When you recognize the vast reach of the remembering self, you can focus on remembering the...