Your returns earn their own returns: a dollar growing 7% becomes $1.07, and next year the whole $1.07 grows, not just the original dollar. Over decades, this creates the hockey-stick curve everyone talks about. But compounding has a silent enemy, and it's not a bad market. It's you, leaving.

Most people assume the key to investing is knowing when to get in and when to get out. Buy before the rise, sell before the crash, repeat. This sounds reasonable. It is also, in practice, nearly impossible — and the cost of trying is enormous. The market's best days and worst days cluster together. Volatility spikes in both directions at the same time, usually during crises, when the news is terrifying and every instinct says to leave. So the investors who sell to 'wait it out' tend to miss the rebound. They catch the crash and skip the recovery.

There's a second, less obvious problem called sequence risk. It's not just about missing the best days — it's about when your bad years land. Two investors can earn identical average annual returns over 30 years and end up with wildly different balances, depending on whether the bad years came early or late. If you get crushed in year 2, you have less capital compounding for the remaining 28 years. A 40% loss in year 2 doesn't just cost you 40% — it costs you 40% of every future gain that money would have generated. The loss multiplies forward through time.

Remember those investors who missed the 10 best days? They weren't unlucky — they were doing exactly what felt rational. The market had just dropped. The news was bad. They moved to cash to protect what they had. Then the market snapped back in a handful of violent days, the way it always does, and they were sitting on the sideline watching it happen. Compounding rewards patience not because patience is virtuous, but because the math requires continuous exposure. Every day you're out is a day your money isn't growing — and a day you might miss the single session that makes your year.