Two years ago I was having breakfast with a man who was purportedly the most successful Jeopardy contestant ever behind Ken Jennings (and the Watson supercomputer). As someone who is always interested in learning new things, I wanted to know how he was able to remember so much stuff.
“Have you ever heard of spaced repetition?” he asked me. “This is going to blow your mind.”
Since that moment, I’ve used spaced repetition nearly every day. I’ve used it to learn and memorize poems, speeches, people’s names, languages and other random facts. I used to think I was just bad with names and birthdays, but I now realize all of that was just a story I told myself.
I learned that spaced repetition is a learning technique that relies on something called the spacing effect. The spacing effect says that it’s easier for you to learn or remember something if it’s repeated over a long period of time (a few months) rather than a short time (one night — i.e. “cramming”).
Using Time and Space to Remember
Think about how memory works for a second. We intuitively understand that there’s a difference between short-term and long-term memory. If I just try really hard for a few minutes, I might be able to remember my credit card number, a stranger’s name, or even a bunch of random facts for a quiz. The problem with this approach is that 24 hours later, I’ve already forgotten most of it. That’s called short-term memory.
Then you have long-term memory, which is where you store stuff like your name, your phone number, the address of the house you lived in when you were a kid, etc. Long-term memory is stuff that stays with you basically forever. It’s possible to forget things in your long-term memory, but it takes a while (or something has to go really wrong with your brain).
But short-term memory and long-term memory are actually two ends of a spectrum. Everything that ends up in long-term memory has to start off in your short-term memory.
One of the most consistent ways that a new fact can move from short-term towards long-term memory is through repetition. Each time you recall something, it moves a little further into your long-term memory. In my limited understanding of how the mind works, I like to think it’s because the neural pathways to this new fact get stronger each time they’re used. (Here is a great graph from a Wired Magazine piece called “Want to Remember Everything You’ll Ever Learn? Surrender to This Algorithm”)
The interesting thing, however, is that the most effective amount of time to wait between repetitions in order to build long-term memory isn’t linear, but exponential.
When someone first tells me their name, I remember it for about five seconds. If I repeat it back to them or in my head a few times, I’ve bought myself probably another five minutes or so. At the end of the conversation, if I say their name as we say goodbye I’ll remember it for another day. If I run into them the next day, then their name will stick with me for about a week, and so on.
In a paper on gradual-interval recall published by Paul Pimsleur in 1967, he hypothesizes the following intervals: five seconds, 25 seconds, two minutes, 10 minutes, one hour, five hours, one day, five days, 25 days, four months and two years. Although the exact intervals varied by subject, Pimsleur’s intervals give you an idea about the exponential nature of memory retention.
One of the cool side effects of this is that you can take a large set of facts (e.g. the 1000 most commonly used words in the French language) and introduce them in batches slowly (e.g. 10 per day). That way you only have to review each word every few months in order to remember them all indefinitely.
There’s an App for That
The good news is that there are tools that will do the spaced repetition part for you. My Jeopardy friend told me about one called Anki that I still use to this day. (The desktop app is free, whereas the mobile app is not.)
In Anki (and most other spaced repetition-based apps) you can either download or create your own sets of flashcards.Every day Anki has you review only a handful of those cards and then you give it feedback about how easy it was for you to remember each card.
I’ll look at a card with just a picture of a friend whose name I want to remember and think “Oh, that’s my friend Steve.” Then I’ll click Show Answer.
Since I pretty easily remembered, it’s clear I’ve seen this card a few times already. Because it wasn’t super easy, I’ll click a button at the bottom labelled “Good“ and I won’t see this card again for another 5.8 months. If I didn’t remember his name at all, then I’d click “Again“ and this card would move back up to the beginning with 10 minute intervals.
I was able to use this system to learn the names and companies of the nearly 150 people in my Y Combinator batch within a few days. My decks currently include: people, quotes and speeches and poems. I try to review each deck for about 10 minutes a day.
At first I got a little carried away and tried to memorize everything, including every language I had ever learned, information from books I was reading and even the Major Mnemonic System for remembering long strings of numbers. The problem is that 10 minutes a day starts to add up as you add additional decks, so I’ve decided to only have three sets going at any given time.
In my people deck I manually create a new card for each new person I meet. Because of my job, I meet a lot of new people in a given week. Remembering names and things about people helps you build rapport. Once I memorized everyone’s name and company in my Y Combinator batch, I was able to truly connect with people on a much more personal level.
The reason I’m memorizing quotes, speeches and poems is because I think it’s fun and useful to be able to pull out an appropriate and articulate quote for any given topic. I think it will be helpful for doing impromptu speeches one day.
If you’re interested in learning more about spaced repetition, there are tons of great articles out there. One of my favorites is Derek Sivers’s post Memorizing a Programming Language Using Spaced Repetition Software. Another must-read is Piotr Wozniak’s 20 Rules of Formulating Knowledge.
A version of this post originally appeared on the author’s blog.
Mattan Griffel is Co-Founder & CEO of Y Combinator-backed One Month, a collection of highly engaging, self-paced courses to learn how to code. He is one of Forbes 30 Under 30 in Education.
The Young Entrepreneur Council (YEC) is an invite-only organization comprised of the world’s most promising young entrepreneurs. In partnership with Citi, YEC recently launched StartupCollective, a free virtual mentorship program that helps millions of entrepreneurs start and grow businesses.