One form of Piketty's equations is r = α × (gpopu + gprod) ÷ s where the five variables are the real return on capital, capital return as a share of total income, population growth rate, productivity growth rate, and savings rate. α approaches 30% today and can't get much higher; gpopu is now much less than 1% throughout the developed world, gprod has slowed. As long as the savings rate (s) holds up, the rate of return on capital is small and getting smaller.
But there's a sort of "paradox" at work. If r = 4%, then a stock paying a steady $4 dividend should be worth $100. But if r is falling or expected to fall to 2%, then the stock will zoom in price to $200. And keep soaring up as long as r is falling. So a general fall in the return on capital assets typically leads to a rise in the price of those assets. Investors make up for their puny dividends and interest with big capital gains. Inflation is low, but interest rates are even lower. The real rate of return on many investments is negative ... and those asset prices keep rising!
If this doesn't make full sense, you're not alone.