What has driven the great U.S. stock boom?

Growth in revenues and profit margins have helped propel the S&P 500 from its lows in 2007 to its recent highs, but growing ebullience has also been a huge factor. The expansion in the S&P 500's price-to-earnings (P/E) ratio has accounted for almost a third of the index's total return. (Percentage contribution of different factors to the total return of the S&P 500 index from September 30, 2007, to June 30, 2024)