Explain Compound Interest So It Actually Sticks

You have heard the phrase. You understand it in the abstract. You still do not feel why it is the most important number in personal finance. This explains it with actual numbers, shows the year-by-year balance growth in a table, explains why time beats rate, and gives one thing to do and one thing to stop doing this week.

Explain compound interest to someone who has heard the phrase many times but still does not really feel why it matters. Use a specific numerical example: someone who invests a fixed amount at a realistic interest rate for twenty years. Show: the total amount invested, the total interest earned, and the year-by-year balance for years 1, 5, 10, 15, and 20 in a small table. Then explain why time is the most important variable, not the amount or the rate. Finally, give one concrete thing someone can do this week that takes advantage of compound interest, and one concrete thing they might be doing that works against them. Under 300 words.