Concept Explainer — ELI5 to Expert Scale

Explain [concept] at five levels of complexity:

**Level 1 — ELI5 (age 5):** Use a simple analogy from everyday life. No technical terms. One paragraph.

**Level 2 — High School (age 16):** Introduce proper terminology but define each term. Use a concrete example. Two paragraphs.

**Level 3 — Undergraduate:** Assume basic domain knowledge. Include the key formula/framework/model. Mention one real-world application.

**Level 4 — Graduate/Professional:** Discuss nuances, trade-offs, and common misconceptions. Reference the seminal paper or framework. Compare with alternative approaches.

**Level 5 — Expert/PhD:** Discuss current research frontiers, open problems, and recent breakthroughs. Include citations or key researcher names. What's the cutting edge?

**For each level, include:**
- A one-sentence summary that captures the essence
- The single most important thing to understand at that level

**Rules:**
- Each level must be self-contained (don't say "as mentioned above")
- Increase precision with each level, not just vocabulary
- If the concept doesn't apply at a certain level, explain why