In the first half of your career, is it more important to earn a high income or to be a good investor? The answer is a good investor–and it’s not even close.

I’ll be a bit more specific. I wanted to analyze how important early career earning vs. investing is for your long-term wealth. The benefit of earning a lot is obvious: you have a lot more to invest. The benefit of investing well is your investments compound at a higher rate. How do these two effects interact?

For the sake of simplicity, I assumed that you are able to invest a certain amount each year for the first 20 years of your career. Then, I looked at how much you would have after 45 years–near retirement–from what you invested in those first 20 years. Finally, I assumed you invest your money through a 401K so you only pay a 40% tax rate at the end.

Let’s take the good investor case. As you hopefully know, I think being a “good investor” means getting the average market return. You don’t need to be Warren Buffet. Since 1957, the S&P 500’s average annual return is 10.67% so let’s assume you get that going forward. And let’s assume you have some money to invest but not a fortune: $10,000 per year. How much do you have at the end of 45 years? A lot! $5.2 million. Compound growth is a magical thing.

Next, let’s look at the high earner case. Instead of compounding at 10.67% per year, what if you instead compounded at what the average American investor gets. There’s no way to sugarcoat this: the average American is bad–really bad–at investing. According to Dalbars, the average American investor only makes 3% per year. If you invested $10,000 per year for 20 years at this rate, you’d only have $348,000 at the end of 45 years. How much would you need to invest each year for those 20 years in order to have more than the good investor? The answer is about $149,000 per year!

Let me state this a different way: you need to invest almost 15 times as much per year if you’re an average investor to have as much wealth at retirement as a buy and hold investor of the S&P 500. 15 times!

Why is the average American so bad at investing? They basically do the opposite of what the index fund buy and hold investor does. They try to pick stocks instead of buying the index. They buy high and sell low instead of just buying and holding. And they pay much higher fees and taxes due to constant trading. Just…don’t do these things.

Einstein apocryphally said that “compound interest is the eighth wonder of the world. He who understands it, earns it; he who doesn’t, pays it.” Good investors understand it–and can do way better than average investors even if the good investor earns a lot less.