Wish you could know where stocks will be in 10 years? Ken Fisher does too! Ken Fisher doesn't think it's possible. Still, people try. There's a notion in academia about the equity risk premium (ERP). The ERP Ken Fisher explains is, literally, the premium you get, expressed as a percentage over some supposed risk-free rate - like the 10-year US Treasury - from holding stocks. Some folks use the T-bill rate. Either way - same basic concept.
And there's nothing wrong with that! It's true - most often investors are rewarded long-term for taking extra volatility risk (done right). And theoretically Ken Fisher notes, investors should be rewarded for suffering through stock market swings. (Although, they hate the volatility. And the more the volatility, the more they hate it when they rationally should love it since, in the long run, they usually get paid handsomely for it.) If you weren't likely to get higher reward for higher risk, why would anyone want the higher risk - whether measured by volatility or otherwise?
The problem with ERPs is some academics try to model future ERPs - predicting future stock returns. Bunk. Ken Fisher has never seen any ERP model stand up to historical back-testing. Not one! Yet, every year, we get a new wave of them.
Find more detail on BUNK 20 in Ken Fisher's Debunkery.