10% is the average annual return the stock markets have produced since 1926. This includes the lowest lows: The Great Depression, the massive slide after September 11th and the financial crisis of 2008.Source: The Basics for Investing in Stocks
…and the average interest rate on most savings accounts is actually below 1% — about 0.06%. People tend to think of saving as the “safer” route, but it’s not that simple.Source
“Returns” are what they sound like — the money that comes back to you from market gains or losses. Leaving in place gives you the opportunity for compounding: earning money on top of the money you earn.
*It's unclear if Albert actually called compounding the “8th wonder of the world” or “the most powerful force in the universe.”Source