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I forgot to schedule a haircut last week. I regularly forget my usernames and passwords. I've forgotten anniversaries, birthdays and promises.

If these confessions sound familiar, it's because we forget all the time. And when we notice we've forgotten, it usually means the thing we forgot was important. Forgetting in these cases is a failing and we naturally wish our memories were more complete. It's no wonder, then, that forgetting has a bad rap.

But we also constantly forget in ways we don't notice — and a lot of this forgetting isn't bad. In fact, it could be crucial to making our memories work as well as they do. That's right: Forgetting can be a good thing.

I don't mean that forgetting can have positive emotional consequences, though there's some evidence for that as well. For instance, most people's memory for autobiographical events is biased towards the positive and positive memories likely contribute to positive emotions and wellbeing. It might be good to forget some of the bad.

No, what I have in mind is more radical still: That forgetting could help us learn from experience and apply what we've learned in real life. To quote William James: "In the practical use of our intellect, forgetting is as important a function as recollecting."

How could this be?

On some views of memory, limitations in remembering don't stem from limited storage space for memories, but from difficulties retrieving memories when they're needed. To take the storage metaphor much too seriously: Having an enormous library isn't very useful if you can never find the book you're after.

Psychologist Simon Nørby puts it well in a recent article on the adaptive value of memory loss: Removing (forgetting) the false, irrelevant or redundant can help reduce "mnemonic clutter." Your library is better without these distractions; fewer tomes in the way of your target. But you also need a good card catalog, and that's where things get most interesting.

Consider the first time you saw penguins and learned that penguins are birds. The experience was probably accompanied by all sorts of sights and sounds and details. Perhaps you were at the zoo on a warm day, with your left hand in the pocket of your favorite striped pants and your right hand in the grip of a parent, who said, in a tired voice, that penguins are birds. You smelled the nearby elephants and you heard the rustle of leaves. You could taste a hint of breakfast — cinnamon French toast — as you ran your tongue along your teeth.

However you first learned about penguins, I bet you don't remember. Or if you do, it isn't at this level of detail. You've forgotten the sights and the sounds, the placement of your left hand, the taste in your mouth. And this might be a good thing. It wouldn't just use up a lot of storage space to encode each experience so finely, it would also be hard to do anything with the subsequent memory. Would you file it under "facts about penguins" or "cinnamon French toast?" Would you re-enact the whole scene every time you encounter new penguins? Or each time you decide whether to put on striped pants?

Removing some of the details — forgetting them — could help extract the generalizable core from an experience and, thus, help you store it in a way that's ready for deployment: useful and likely to be called up when needed. Indeed, to appreciate the value of forgetting, consider what would happen if forgetting failed.

In a well-known story, Jorge Luis Borges introduces Funes the Memorious, a character who could not forget. He was mired in particulars; unable to abstract away from experience. The narrator tells us that Funes could reconstruct an entire day from his past, but it would take him a full day to do so, each memory unfolding with the richness and detail of the original experience. He tells us that Funes had trouble appreciating that dogs of different breeds shared something in common (for instance, being dogs), and even that the same dog, viewed from different angles or at different times, was the same individual. "To think," the narrator tells us, "is to forget differences, generalize, make abstractions. In the teeming world of Funes, there were only details, almost immediate in their presence." Funes himself compares his memory to a garbage heap. All details, no card catalog.

Borges was writing fiction in the 20^th century, but he got some things about human psychology right. In his review of the latest empirical research, Nørby tells us that forgetting "is a positive force that helps people focus on the now and the next," not — like Funes — on the particulars and the past.

If we had infinite processing capacity — not only an infinite library, but infinite time and infinite computational power — perhaps we could afford to forget less, or not at all. We could maintain the details just like Funes, and also generate abstractions. But being the bounded creatures we are, forgetting isn't merely a bug, it's a design feature.

This doesn't imply that every instance of forgetting is good. In fact, the ones we notice are typically bad. But then there's the forgetting we take for granted, and for much of that, we should be grateful — even if that haircut is long overdue and the birthday card never makes it to the mail.

Tania Lombrozo is a psychology professor at the University of California, Berkeley. She writes about psychology, cognitive science and philosophy, with occasional forays into parenting and veganism. You can keep up with more of what she is thinking on Twitter: @TaniaLombrozo