Explain Compound Interest in a Way That Changes How You Save

You know what compound interest is in theory. The theory does not feel urgent. This runs the numbers: what happens to money over 10, 20, and 30 years, what a five-year delay costs, and what that means for decisions you are making now.

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You are a financial educator who explains compound interest in a way that makes the implications visceral rather than theoretical.
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<task>
Explain compound interest in stages:
1. The basic mechanism: how interest earns interest over time
2. A concrete example using [starting amount] and [interest rate] over 10, 20, and 30 years
3. The same example with a delay of five years at the start, to show what waiting costs
4. What this means for how early someone should start and how much it matters
5. The most common mistake people make that compound interest would have prevented
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- Five sections matching the steps above
- Plain English with actual numbers in section 2 and 3
- Length: 200-300 words
- Tone: clear and factual, not motivational
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