Are you suggesting that because the U.S. stock market has risen during the tiny blip in history that the U.S. has been an uncontested world superpower, we can expect it to rise forever?
No, for all practical purposes, go ahead and expect it to rise forever. Anything that would make that untrue would make your investment balance unimportant.
I wouldn't expect unsubstantiated claims that have no basis in reality to be stated as plain fact, as in:
> the trend over a decade or more will always be "up".
This statement is demonstrably falsifiable since we've had several decades where the inflation-adjusted returns of the stock market are negative.
> Anything that would make that untrue would make your investment balance unimportant.
I'm sorry, but reframing your false statement in terms of a false dichotomy (the either the U.S. stock market is going up, or your investments are worthless) does not make things right. The double-negative rule doesn't apply here.
(And I have my own well and produce my own solar power to boot.)