Why Do We Forget? The Forgetting Curve and Science-Backed Ways to Remember

The name of someone you met yesterday, exam material a week after the test, why you walked into the kitchen — forgetting is something we all do every day. We usually see it as a flaw. But to scientists, forgetting is not a malfunction of memory; it is a natural part of how memory works. Understanding why we forget also teaches us how to remember better.

Ebbinghaus’s experiment on himself

The first person to measure forgetting scientifically was the 19th-century German psychologist Hermann Ebbinghaus. To stop meaningful words mixing with what he already knew, he invented nonsense syllables such as “DAX”, “BUP” and “ZOL”. He made lists of them and studied each until he could recite it perfectly.

Then he waited for different lengths of time and relearned the lists, measuring how much quicker relearning was than the original learning — the “savings”. His results, published in 1885, became the basis of what we now call the forgetting curve.

The most striking thing is the shape: forgetting is very fast in the first hours, then slows. In Ebbinghaus’s data, savings fell to 58% after just 20 minutes and to 34% after a day. After a month, they were down to about 21%.

In 2015, researchers at the University of Amsterdam repeated Ebbinghaus’s experiment using the same method and obtained a very similar curve. A 140-year-old finding still holds.

Of course, nonsense syllables are forgotten far more easily than real-world information. We remember meaningful, interesting things linked to what we already know for much longer. But the general shape of the curve shows up in almost every kind of learning.

Why do we forget? Five main reasons

Psychologists do not explain forgetting with a single process. Several mechanisms work together.

1. It was never stored

Sometimes what we “forget” we never learned in the first place. A name heard while our attention was elsewhere never makes it into memory. Try this: draw both sides of a coin you use every day in detail. Most people cannot, because we never pay attention to those details.

2. The trace fades

Unused memories can fade over time — the oldest explanation for forgetting. It is not enough on its own, though, because an ordinary memory from years ago can suddenly come flooding back with a smell or a song.

3. Memories interfere

Research shows that one of the biggest causes of forgetting is interference:

• Old information disrupts new: while learning your new phone number, the old one keeps popping up.
• New information disrupts old: as you learn a new language, you may struggle to recall words from one you learned earlier.

Similar information interferes most. Two similar subjects studied back to back on the same day disrupt each other the most.

4. The information is there but unreachable

Much of what we think we have forgotten is actually still in memory; the problem is retrieval. The tip-of-the-tongue feeling is the best-known example: you know the first letter, the length, even words it sounds like — but not the word itself.

Remembering depends on finding the right cue. That is why recall gets easier when you return to the place where you learned something or are in the same mood.

5. The doorway effect

Walking into a room and forgetting why is a very common experience. Gabriel Radvansky and colleagues at the University of Notre Dame studied it experimentally. Participants carried objects in virtual or real environments; after walking through a doorway, they found it harder to remember what they were carrying than people who walked the same distance within one room.

The researchers suggest the brain treats doorways as event boundaries. When a new scene begins, information from the previous one is “archived” and becomes harder to access.

Forgetting is actually useful

You might think it would be great to remember everything. But forgetting has real benefits:

• It filters out trivia: your brain prefers to keep who you talked to at lunch, not how many forks were on the table.
• It prioritises current information: forgetting where you parked last week makes it easier to remember where you parked today.
• It enables generalisation: letting go of details helps us draw common lessons from experiences.

The very rare people who forget almost nothing describe it as sometimes exhausting and overwhelming.

Science-backed ways to slow forgetting

The good news: the forgetting curve can be bent. Psychology research shows several methods are especially effective.

Spaced repetition

Instead of studying something once for a long time, reviewing it several times with gaps in between produces far more durable learning. A large 2006 analysis combining hundreds of studies confirmed that this effect is extremely robust.

After each review the memory becomes sturdier, and you can wait longer before the next one. Reviewing something the day after learning it, then three days later, then a week later is a good start. Many language-learning apps work on this principle.

Testing yourself

In 2006, Henry Roediger and Jeffrey Karpicke at Washington University in St. Louis split students into two groups. One group reread a text several times; the other read it once and then tried to write down everything they remembered.

In the short term, the rereaders did slightly better. But a week later, the self-testing group remembered far more. This is called the testing effect: the act of trying to recall strengthens the path to the memory.

Making meaning and connections

Linking new information to what you already know gives you more than one route to it. Explaining a concept in your own words, finding examples or teaching it to someone else all strengthen memory.

Sleeping well

During sleep the brain replays what it learned during the day and transfers it into long-term memory. People who sleep after learning remember more than those who stay awake for the same time — which is why pulling an all-nighter before an exam often backfires. We cover this in our article Why do we dream?.

In short

We forget for different reasons: information is never stored, fades over time, gets mixed up with other memories or becomes hard to retrieve. Ebbinghaus’s forgetting curve shows that we lose much of what we learn in the first hours. But spaced repetition, self-testing, making connections and good sleep can slow the curve dramatically. Forgetting is not the enemy of memory — it is part of how memory selects what matters.