Aswath Damodaran has estimated the implied equity risk premium on the S&P 500 to hover in the range from 3.5% to 6.5% over the last decade: https://pages.stern.nyu.edu/~adamodar/New_Home_Page/home.htm . So it's in the ballpark of how an average stock is expected to perform. (And as a sibling comment says, actual realized performance was even better over the last decade.)

If only, say, 3% annual returns above the interest rate were projected on a project, it would be clearly below the line of viability. There would be no reason to bother with the hassle and risk: just park your money in an index fund.