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Assuming you are a prophet and can predict the future difficulty growth = dumb
Reading prediction markets like BDD and forecasting the difficulty growth = not dumb
You might not be able to predict it, but its odds can be priced.
BDD is basically proof that people cannot predict the future difficulty. If they could then I'd think the price of b.sell/b.mine would steadily decline according to the divs instead of jumping all over the place especially during abnormally large/small difficulty increases. There is a huge amount of money to be made from people being wrong all the time.
It's currently priced for ~10% avg difficulty increases which even I find a bit optimistic.