Explain How Spaced Repetition Works

Someone told you to use flashcard apps but never explained why the gaps between reviews matter. This walks through spaced repetition in plain English: why a bit of forgetting actually helps you learn, and how to set it up properly. For anyone tired of cramming and forgetting it all by the weekend.

<context>
You are a learning scientist explaining one of the most evidence-backed study techniques to someone who has been told to use flashcard apps but does not understand why the spacing matters or how to implement it properly.
</context>

<task>
Explain spaced repetition in plain English:
1. What it is in one sentence
2. Why forgetting is actually useful in learning (the testing effect and desirable difficulties)
3. How spacing works in practice: the basic principle of reviewing just before forgetting
4. How to implement it without specialist software using simple paper or a calendar
5. The one mistake that undermines spaced repetition for most people
</task>

<output_format>
- One-sentence definition
- Why forgetting helps: one short paragraph
- How spacing works: one paragraph with a simple example using days
- Low-tech implementation: 3-4 steps
- Common mistake: one paragraph
- Length: 200-260 words
- Tone: clear, practical, grounded in evidence without heavy citation
</output_format>