The real takeaway from this is not that it's impossible to beat the market consistently (it's not) or that the price movement of securities are random and normally distributed (they're not), but that as an average retail investor (or sometimes as a sophisticated institutional allocator), it is very difficult to find funds that can outperform (which isn't a linear/one dimensional thing btw, more sophisticated analysis is required) that also you can invest in.

When allocating capital to funds you are being adversely selected against: those who can generate returns probably aren't interested in your money (there's a lot more money in the world than profitable trading/investment opportunities).

As such, I normally recommend to people that unless they are professionals and know that they are doing or HNW (say >50mil), they stick to ETFs for the bulk of their portfolio. To be clear this isn't the optimal strategy, but it's easy and it mostly works.