I listened to a podcast that alluded this study, so I looked it up. "When stated in terms of lifetime dollar wealth creation, the best-performing 4% of listed companies explain the net gain for the entire US stock market since 1926, as other stocks collectively matched Treasury bills." Out of the 30,000+ stocks that have existed in US Markets, 4% made up the entire net gain since 1926. We already knew this, but seeing it put that way is astounding. (If the link doesn't work, it's "Do Stocks Outperform Treasury Bills" by Hendrick Bessimbinder, Sep. 2018).

https://www.sciencedirect.com/science/article/abs/pii/S0304405X18301521