Have you ever spent all night cramming for a test, aced it, and then realized two weeks later you'd forgotten almost everything? This is the "binge and purge" cycle of learning. It gets you through the test, but it doesn't build knowledge. Enter Spaced Repetition: the algorithm for wisdom.
The Forgetting Curve
In the late 19th century, German psychologist Hermann Ebbinghaus memorized thousands of nonsense syllables to map how memory fades over time. He discovered that memory decay is exponential. Without review, we forget about 50% of new information within 24 hours.
"Spaced repetition turns the forgetting curve into a retention curve."
How it Works
The principle is simple: review information at the moment you are about to forget it.
If you review too soon (e.g., 5 minutes later), it's too easy and doesn't strengthen the memory. If you review too late, you've already forgotten it and have to relearn from scratch. But if you review it just right—when it's a struggle to recall—your brain reinforces the memory significantly.
The Schedule
A typical manual spaced repetition schedule might look like this:
- 1st Review1 day later
- 2nd Review3 days later
- 3rd Review1 week later
- 4th Review1 month later
Automating Spaced Repetition
Keeping track of what to review and when in a spreadsheet is tedious. That's why software is essential. Tools like Anki and selftest.in handle the scheduling for you. When you take a quiz on selftest.in, identify the topics you struggled with. The platform helps you generate new questions on those specific weak points in your next session.
The "Interleaving" Bonus
Don't just space out your practice—mix it up. Instead of studying only History for 3 hours, study History, Math, and Biology in interleaved blocks. This "context switching" forces your brain to constantly reload different schemas, which, like active recall, strengthens long-term retention.