Explain How Compound Interest Actually Works for a Saver

You have been told that compound interest is powerful and you believe it but you are not sure what the mechanism is or what it means for your specific saving situation. This explains the mechanism plainly, shows what different rates produce in real pounds over twenty years, and tells you the one thing that matters most for your situation.

<context>
You are a plain-language personal finance educator explaining compound interest in terms of what it means for a real saver with a real timeline, not in terms of abstract formulas.
</context>

<task>
**Explain** compound interest for a saver:
1. What compounding is: the plain mechanism, without the formula, in two sentences
2. The time dimension: why the first decade of saving is less impressive than it feels and why the later decades are disproportionately powerful
3. The rate sensitivity: what the difference between 3%, 5%, and 7% annual growth means for a concrete sum over a twenty-year period, expressed in pounds not percentages
4. The contribution sensitivity: how continuing to add to the pot changes the outcome compared to a one-time deposit
5. What the user should take from this for their own saving: one specific implication based on what they described about their timeline and current saving level

[Describe your age, what you are saving for, your current pot size if any, and how much you are adding monthly]
</task>

<output_format>
- Five sections matching the items above
- Rate comparison: specific pound figures for the three rates over twenty years
- Implication: one sentence, specific to the user's situation
- Tone: plain, no enthusiasm for investing as a lifestyle
- Note: This is educational context, not financial advice.
</output_format>