[This is #2 of a series of Meditations on Risk.]
As a follow up to the last post about basing our decisions on the recent past, here is the bad news:
Long-term investing is not long enough
We only have 82 years of data. As funny at this sound, 82 years is not a lot. They are still arguing about global warming and we have hundreds [if not thousands] of years of temperature data.
So for us to pretend that the equity premium is the birthright of anyone willing to stay the course for 10, 20, or even 30 years might be something we want to reconsider.
All we have is 82 years of data. There is still a lot we don’t know. The reason investing in the stock market is risky is not because it moves up and down a lot (standard deviation), it is because things change in unexpected ways. What worked for the last 20 years may not work next year (ask the guys at Long-Term Capital).
I am not saying that 82 years of data is worthless, I am just suggesting that we move forward with a sense of caution instead of a false sense of precision.