⏳ Mental Models for Money #2: The Power of Compounding

I want to continue a recurring segment in this newsletter called Mental Models for Money.

These aren’t tactics or rules. They’re ways of thinking that help you focus on what actually matters, without needing to be an expert or constantly disciplined.

Last time, we talked about the Pareto Principle (focusing on the few things that drive most results). This week, we’re talking about compounding: the reason time matters more than intensity in investing.

In today’s edition, we’ll go over:

• What Compounding is

• What This Means for Your Personal Finances (and How to Use It)

• How This Applies to Investing (and to Life)

TLDR;

The Bottom Line

Compounding rewards time more than effort. Starting earlier, staying invested, and avoiding interruptions matter more than chasing higher returns. The longer your money stays in the system, the more it works on itself.

The content

Compounding Explained

Compounding happens when the money you earn starts earning money too. You invest, it grows, and instead of withdrawing the gains, you leave them in. The next year, you earn returns not just on what you invested, but also on the previous gains. Over time, that snowball gets bigger.

To make this concrete, let’s assume an 8% annual return and that you invest until age 65.

Even when the 30-year-old invests more in total than the 20-year-old, they still end up behind. Even when the 40-year-old invests triple the annual amount, the gap remains large.

What This Means for Your Personal Finances (and How to Use It)

Time vs Timing in the Market

Compounding works better with time than with perfect timing. You don’t need to predict market highs and lows. You don’t need to trade every week. You just need to stay invested long enough for your money to grow on top of previous growth.

Every time you stop investing, pull money out too early, or switch strategies, you slow that growth down. Even short breaks can reduce momentum.

For passive investors, this is good news. You don’t have to watch charts or react to every headline. Compounding works best when you:

• Invest regularly

• Reinvest what you earn

• Keep fees low

• Avoid constant switching

Fees grow over time too. A small 1–2% difference each year can mean a much smaller portfolio decades later.

Stay invested long enough, and time does most of the work.

Why should you care?

How This Applies to Investing (and to Life)

In investing, compounding shows up clearly in long-term index funds or dividend reinvestment. Left alone, they build momentum.

The same pattern applies elsewhere.

• Skills compound when you practice consistently.

• Networks compound when you nurture relationships.

• Reputation compounds when you deliver steadily.

Early progress feels slow. Then stored effort becomes visible. What looks like overnight success is often accumulated cycles finally showing up.

The middle years are where compounding accelerates, and that acceleration only happens if you stay through the slow beginning.

A Way to Reflect on This

Ask yourself: where am I interrupting compounding?

Are you starting and stopping investments? Pulling money out too early? Changing plans every year?

Then ask the opposite question: what would happen if you left one solid system alone for ten years?