Why do we always forget what we have learned? (The Forgetting Curve)

How to use the Forgetting Curve and Spaced Repetitions to remember everything?

The forgetting curve shows how quickly we forget new knowledge. The curve was discovered in 1885 by the German psychologist Hermann Ebbinghaus. In this article, I will show you:

• why we forget things,
• how the forgetting curve is structured
• how you can build up a personal knowledge store through spaced repetitions (spacing effect) so that you can finally keep all the important facts in mind.

I often think to myself that my mind is like a sieve: Luckily, I am not alone! Most people instantly forget most of the things they have learned. In fact, it is estimated that in the long term we can just remember about 15% of the things we have learned.¹

However, just a minority of people are trying to improve their recall rate. At university, most students rely on bulimia learning (cramming) to get the facts into their heads. But cramming is a short-term solution. Long term your recall rate will be even worse with cramming.²

When I was a student, I also relied mostly on cramming before exams. However, anyone who asks me today about the things that I learned in my business degree will quickly see that just a few facts have actually stuck with me: In truth, just the facts that play a role in my life and in my job today (and that is only a small fraction of the entire curriculum).

We always forget …

… and that’s not necessarily a bad thing. Our brain needs to make room for new knowledge and therefore only tries to keep relevant information that is important for our lives. Therefore, things that have an impact on our lives stick better in our brains.

But are once forgotten things really gone? Surprisingly no:

Every piece of information we’ve ever learned is stored in our heads. It seems that we only need a key to bring it out again because humans remember by linking thoughts.

What did we do on July 4th, 2017? I have no idea, because I am missing the link to this date.

However, if you ask people who have consciously experienced eventful days like September 11, 2001, or November 9, 1989, in Germany, they can almost always remember also the unimportant things that they did on that day.

The emotional events of those days serve as a connection to all the other memories associated with it

Learn smarter, not harder (Mnemonics)

There is not always a life-changing event going on that could serve as a memory anchor for the knowledge we are currently learning. And this is a good thing!

Still, there are many methods of converting dry facts into pictorial and emotional information to slow down the forgetting. The two most prominent of those mnemonic techniques are the loci method and the major system.

The only issue with these methods is that they are relatively laborious to set up.
In addition, mnemonic techniques do not stop forgetting knowledge, they just slow this process down: The information stays in the brain longer because stronger neural connections are established, but whoever neglects to call up this memory will still have difficulties, in the long run, finding the stored information.

I am a big fan of mnemonics and they are also the reason why I got interested in memory training and learning methods in the first place. However, they are not a panacea when it comes to gaining knowledge over the long term.
For a long time I gave up trying to find a solution. Instead, I tried to save new knowledge in such a way on my computer that I could access it again quickly.

It became less important to me to remember the facts, instead I tried to memorize the location. This outsourcing was not satisfactory, because without a computer or smartphone there was no way to access the information and in fact I often forgot the storage location.

In 2019, however, I accidentally discovered a learning method that now allows me to store new knowledge in a much more sustainable way. This method is mostly called “Spaced Repetition”.

Ebbinghaus discovers the Forgetting Curve

It takes advantage of the forgetting curve (also called the spacing effect) by trying to repeat facts at the right time. This way you can remember facts just by doing a few repetitions, which are spread over several years.

We do not forget information linearly, but exponentially: We have the greatest loss of knowledge in the first few minutes, then the curve slowly flattens out.

On average, after half an hour, half of the learned facts disappear again. And so it goes on: Every new knowledge is lost with a half-life of 30 minutes. After 6 days we can only remember 23% of the subject matter. In the long term, only 15% of the learned facts remain stored in the brain and of course, we cannot choose which facts belong to this 15% at the end of the day.³

The course of this forgetting curve was presented for the first time by the German psychologist Hermann Ebbinghaus. He tested his memory by learning lists of meaningless syllables (according to Wikipedia: pöt, tuv or zim) and then checked how quickly he forgot the syllables he had learned.

He was able to demonstrate the exponential course of forgetting.

Ebbinghaus proofed that people forget new knowledge with a half-life of 30 minutes.

That at least explained why so many people feel like their mind is a sieve in their heads, but much more important was his second finding:

The beauty of Spaced Repetition

When Ebbinghaus repeated his list of syllables the following day, he was able to memorize it perfectly with significantly less learning time. After each repetition, he could increase the distance between the repetitions in order to achieve the same learning success (the distance between the necessary repetitions also increased exponentially).

Today we call this phenomenon the spacing effect. The spacing effect decreases the time we need for learning because it makes learning more efficient when we know the optimal time interval between each repetition.

However, since forgetting, among other things, is influenced by:

• The complexity of the matter
• Our motivation
• The embedding of the material in existing knowledge

Therefore, no universal forgetting rate exists. Each subject has a different forgetting rate (depending on its complexity), so it would be virtually impossible to determine the ideal repetition periods for facts on your own.

However, it is possible to determine the repetition intervals with the help of an algorithm. Since the 1980s we have educational software that tries to solve exactly that: It all started with the Supermemo program by the Polish researcher Dr. Piotr Wozniak. Far better known today (especially among law and medical students) is the open-source software Anki.

This is how Anki and Supermemo improve your memory

Learning software like Anki or Supermemo tries to determine the correct repetition time using an algorithm.

If you learn a new Anki card, it will be shown to you again after a day. If you can recall it on the first repetition, the interval increases (the interval depends on whether you found the answer difficult or easy). If you can’t remember, you’ll have to repeat it again the next day.

The Anki algorithm is certainly not 100% perfect, but that is often due to the user: Perhaps she regularly skips repetition days or states that the answer was easy for her, although she had difficulties answering it.

Nevertheless, with the help of Anki, everybody can learn new knowledge relatively efficiently and remember facts long term.

Today, Anki is part of my personal knowledge store (besides my Zettelkasten): Regardless of whether it is information from books, blogs, YouTube videos, or lectures when I think that the knowledge will be beneficial for me in the future, I will create an Anki card for it.

This way I can be sure that I can remember it later, as long as I do my Anki repetitions that just take some minutes every day.

That is also the only problem with learning with Anki: If you want to keep knowledge for a lifetime and not just until the next exam, it has to be repeated for a lifetime.

However, that sounds more exhausting than it really is: After just a few successful repetitions, the interval until the next
repetition increases to several years. If you would not add new cards to your Anki stack, you would soon have little to do.

In my experience, however, most people take a different route and add new knowledge, far too quickly and on far too large a scale.

If you are overwhelmed, you can quickly get an Anki burnout. But this is the topic for one of my next articles.

[1]: Prof. Dr. Werner Stangl. (Seen on 22.11.2021). Die Vergessenskurve. https://arbeitsblaetter.stangl-taller.at/GEDAECHTNIS/Vergessen-Ebbinghaus.shtml
[2]: BBC. (Published on 17.09.2014). https://www.bbc.com/future/article/20140917-the-worst-way-to-learn
[3]. Prof. Dr. Werner Stangl. (Seen on 22.11.2021). Die Vergessenskurve.. https://arbeitsblaetter.stangl-taller.at/GEDAECHTNIS/Vergessen-Ebbinghaus.shtml).