Why the things we love become invisible

Representational Pics/istock

The sound of traffic outside your window. The particular smell of the grocery shop on the corner. The person who sits on the same bench every morning.

Then you live there for a year. One morning you walk past the same building without seeing it. Nothing has changed.

You have. I started thinking about this because of something much smaller. Sitting in my room one evening, I suddenly noticed the hum of my refrigerator. It had probably made the same noise for years, and I had never really heard it.

Then I couldn't stop hearing it. It made me wonder about a phrase we use all the time: you get used to things. We usually mean that familiarity makes something less interesting. That felt too easy, so I started reading about how the brain handles repetition.

What I found was more interesting. The brain is not simply recording what is happening around us. It is constantly trying to work out what will happen next. That sounds like a small distinction. It isn't.

Imagine walking into your kitchen tomorrow to find the refrigerator where it has always been. You barely register it. Now imagine finding it standing in the middle of your living room. You would remember that morning forever.

The refrigerator hasn't changed. Your expectation has. Your brain had predicted where it should be, and reality disagreed. That disagreement gets your attention. Neuroscientists call this mismatch a prediction error. The brain constantly compares what it expects with what it receives, and updates its model when they differ. It happens that we experience the result simply as normal or strange. We don't think, my predictive model has just been confirmed. We just don't notice the refrigerator.

That explained why the new city had looked so vivid. Nothing in it was more beautiful. Almost everything in it was unpredicted. With no model of the street, my brain gave every shop sign, traffic light, and strange noise a little attention.

A year later, the same street had become a prediction. And once the brain knows what comes next, it stops announcing it to you. Think about the sounds of someone you live with. At first you notice everything: the way they close a door, their footsteps in the corridor, the sound of their laugh. Eventually you stop hearing them. But let that person make one unusual sound in the middle of the night, and you wake up. Your brain knows this is not what usually happens next.

The same is true of our bodies. You don't notice your heartbeat until it races. You don't notice your breathing until it becomes difficult. You don't notice the air conditioner until it stops, or the person beside you on the train until their seat is empty. This is where the science starts to say something about how we misunderstand our lives.

We often assume familiarity makes things less valuable. Perhaps it doesn't. Perhaps familiarity simply makes things less informative. In information theory, an event carries information roughly in proportion to how surprising it is. If I tell you the sun rose this morning, I haven't told you much. If I tell you it didn't, you have learned something extraordinary.

Our brains seem to run on a similar economy. The more reliably something happens, the less attention it demands. That is useful. Otherwise you would have to consciously process every chair, every passing car, every breath. So the brain lets the familiar fade into the background. It is a wonderful system. It is also slightly cruel. Because some of the things that fade are precisely the things we care about most.

Your mother's voice. The person who sleeps beside you. The road home. The dog waiting near the door. The cup you use every morning. The light through the same window. They haven't become less remarkable. Your brain has simply become extremely good at predicting them. And then something happens. The person moves away. The dog is no longer there. Your mother doesn't call one evening. The house becomes quiet.

And suddenly you notice what had been invisible. I think this is partly why absence feels so physically strange. When someone leaves your life, you don't only lose their presence. You lose a huge number of predictions: where they should be, when they usually call, what they will probably say when you tell them something. Those predictions keep arriving after the person has gone. You walk into a room expecting someone who isn't there. You reach for your phone at the time they used to message.

For a while, your brain lives slightly in the past. It has learned a world that no longer exists. Perhaps this is why grief can make familiar places feel unfamiliar. The furniture hasn't moved. The street hasn't moved. But the world has stopped behaving the way your brain expected. There is something beautiful here too. The same mechanism that makes a familiar street invisible is what allows us to become experts.

A physicist sees things in a spectrum that I would miss. A musician hears a note that is slightly wrong. A doctor notices something unusual in a scan. A parent hears in a child's voice that something is wrong before the child says a word.

Expertise is not simply knowing more facts. It is having a better model of what normally happens, and therefore noticing when reality departs from it. The strange consequence is that the better you know something, the less of it you consciously notice, except when it changes. This is true of a laboratory, a city, a marriage, a life.

Perhaps this is why we occasionally need to leave the places we love. Not because they have become less beautiful, but because we have become too good at predicting them. Return after a year and the old street is visible again. The café looks different. The trees seem taller. Nothing has become new. You have simply lost the prediction.

I think about that refrigerator sometimes. It was there every day, doing exactly what it was supposed to do. My brain had simply stopped reporting it to me. There is something both comforting and sad in that.

Perhaps the things we love don't become ordinary because they matter less. They become ordinary because they become dependable, and dependability is precisely what allows the brain to stop looking.

Maybe that is why an unfamiliar day can feel so alive, and an ordinary one can pass without leaving a trace.

The world does not become less interesting as we grow familiar with it. We just become better at predicting it. And sometimes, when the prediction breaks, we suddenly see what had been there all along.

Nishant Sahdev is a physicist at the University of North Carolina at Chapel Hill. He chases ideas that refuse to stay in laboratories, for your favourite Sunday mid-day.