There is a distinction between small stock investors who buy and hold for long term gains, and small traders, who aim to make many small, quick gains and must compete with the market distorting manipulations of large traders. Cautious small investors can do well, sometimes remarkably well.
I place my wife and myself in the "remarably" well class over the past 5 years and over the past 40 years, very well.
Perhaps the super rich do better over all but we are happy with our gains.