Why We Forget Things, and How Memory Really Works

Memory isn’t a video recording. It is closer to a set of notes the brain rewrites and prunes all the time. Seen that way, forgetting isn’t a fault. It’s part of the design.

Memory in three steps

To remember something, three things have to go right:

1. Taking it in (encoding). You have to notice the information and pay attention to it.
2. Keeping it (storage). The brain has to strengthen it into a lasting memory. Much of this happens later, including during sleep.
3. Finding it again (retrieval). You need a way back to it: a cue, a question, a place, a smell.

Forgetting can happen at any of these steps, and each one feels different.

The forgetting curve

In the 1880s, the German psychologist Hermann Ebbinghaus tested his own memory by learning lists of made-up syllables and measuring how much effort it took to relearn them later. He found that memory drops steeply at first and then levels off. Most of what is lost goes within the first hours and days. What survives that period tends to last.

This pattern is called the forgetting curve. In 2015, researchers at the University of Amsterdam repeated the experiment as closely as they could, with one person learning 70 lists over about 70 hours. They got a very similar curve.

You’re most likely to lose new information soon after you learn it. That is also the best time to go back over it.

Why memories slip

Researchers describe several everyday kinds of forgetting:

• Fading. Memories that aren’t used weaken over time. Brain scientists see this as useful, because it clears out details you no longer need.
• Never stored in the first place. If your mind was elsewhere when you put your keys down, the memory was never properly made. This is the usual reason for losing things and for walking into a room and forgetting why.
• Blocking. The memory is there, but you can’t reach it. A name on the tip of your tongue is the classic example. It often comes back later, once you stop trying.
• Interference. Similar memories get in each other’s way. Your new phone number is hard to learn because the old one keeps turning up, and the reverse can happen too.

What actually helps

Test yourself instead of rereading

Pulling a fact out of memory strengthens it more than reading it again. In a well-known 2006 study, students who read a passage and then tried to recall it remembered more a week later than students who spent the same time rereading, even though the rereaders felt more confident.

For everyday life: close the book and say what you remember, or use flashcards.

Spread it out

Short sessions spread over days beat one long session. A 2006 review covering 317 experiments found a consistent benefit from spacing practice out, and that the longer you need to remember something, the longer the gaps should be.

Protect your sleep

Sleep is when the brain strengthens new memories and files them for the long term. A large review of sleep research concluded that sleep, and deep sleep in particular, helps new memories last. Our guide to how much sleep you really need covers the basics.

Pay attention on purpose

Many “memory problems” are attention problems. Say a new name out loud, look at where you’re putting your keys, or do one thing at a time. See why multitasking makes us slower.

Use the outside world

Lists, calendars, reminders and always keeping things in the same place aren’t cheating. They free your memory for things that matter more.

When forgetting is worth checking

Some forgetfulness is a normal part of getting older, such as taking longer to recall a word or sometimes misplacing things. The US National Institute on Aging suggests talking to a doctor about signs such as:

• asking the same questions over and over
• getting lost in places you know well
• trouble following recipes or directions
• growing confusion about time, people and places