Most people forget 80% of what they study within a week. Spaced repetition fixes that.
In 1885, psychologist Hermann Ebbinghaus discovered that memory decays in a predictable pattern. Without any review, you forget roughly half of new information within a day and around 80% within a week. This isn't a personal failing — it's how human memory works by default. The question is whether you study in a way that works with this pattern or ignores it.
Spaced repetition is a study technique that schedules reviews at increasing intervals — timed to occur just before you would naturally forget something. The first review might come a day after learning. The next, three days later. Then a week. Then a month. Each successful review extends the interval further. The concept is being reinforced at exactly the moments it needs reinforcement — not wasted when it's fresh, not missed when it's fading.
Mathematics is a cumulative subject. Every new concept depends on previous ones. If you forget what a coefficient is, algebraic manipulation stops making sense. If the rules of fractions are hazy, anything involving rational expressions becomes guesswork. Spaced repetition doesn't just help you remember — it keeps your entire mathematical foundation solid, so each new concept has stable ground to build on.
Every concept introduced in a MathJourney lesson is tracked individually. As you work through exercises, the system records your performance — how quickly you answered, how often you've gotten it right, how recently you reviewed it. This data drives a scheduling algorithm that determines exactly when each concept should be shown to you again. The queue adapts to your specific memory, not a generic model. Concepts you find easy space out over weeks. Ones you struggle with come back sooner.
The real power of spaced repetition isn't visible in a single session — it's visible over months. Concepts you learned six months ago stay accessible. Your mathematical vocabulary grows without constant revision. The knowledge you've built doesn't rust. Students who use SRS consistently report that their older material feels as solid as their recent learning, which is exactly the point. You're not building a house of cards. You're building something permanent.