The only way to truly take the randomness
out of the stock market is to have a
multi-decade time horizon.
He says so after looking at the data of a few decades. That makes no sense. It is like looking at 3 people and saying "People come in groups no larger than 3".The whole article is based on that premise. He has something like 90 data points and assumes the next 90 data points will be alike.
Is it possible the next 10 years will have a negative return? This is a very interesting question. But I doubt we can answer it by looking at historical returns. We need to look at the actual situation. What would have to happen in the world so we see negative returns? War? A natural desaster? Who says war and natural desasters cannot throw us back 100 years? 1000? 10000?