There’s trouble on the horizon for private equity. As the 50-year-old industry matures, investment returns are falling. In fact, for the past three decades, average buyout performance — the return a buyout firm generates from buying, improving, and then selling a company — has been on a downward trend. A study by Harvard professor Josh Lerner, State Street, and Bain, for example, found a meaningful drop of six percentage points between the 10-year annualized return in 1999 and the comparable return in 2019.