On the other hand, it's hubris to think we can predict the future.

Sounds good in general, but I think it depends on what the prediction is. I'm pretty confident in asserting that the profits of the broad US equity market won't ever exceed its revenues, in the same way that I predict you can't ever get two gallons of water into a one gallon bucket.

So the recent trend of rising net profit margins will end at some point and, even if they stay at their peak, profits would grow no faster than sales thereafter. S&P 500 real sales have risen 1.57%/year in the last 25 years and 2.48%/year in the last 15. You get dividends on top of those capital value growth rates, but since prices are so high the yields are low: 1.14% at the moment, and that's well above long term trends.

Other than the 2017 tax rate cut, Berkshire's return has managed to keep up without unsustainable tail winds like rising valuation multiples or a temporary profitability supercycle. It hasn't been a perfect result and it might lose some steam, but it's still a pretty good machine.

Jim