That's a fair counterargument, but I don't think it holds up. I'm talking about a portfolio rather than a single asset. Technically we would want to model that

That's a fair counterargument, but I don't think it holds up. I'm talking about a portfolio rather than a single asset. Technically we would want to model that using a log-normal distribution, but I think the example suffices. Can you think of a realistic example where someone would accidentally hold a dynamic portfolio that exhibits outperforming returns over 20 years?