I wouldn&#x27;t put a lot of faith in such predictions either, but there are a few reasons to believe that exceptionally good returns might not be repeatable. One is simply regression to the mean. Others are high global levels of debt and a significant wave of globalization having just run its course.<p>But I think productivity growth and our ability to redistribute the fruits of that productivity growth are the big unknowns for the next 20 years. The current step change in our AI capabilities could throw a spanner in all attempts at making any reliable predictions.