“Past performance does not guarantee future success” but about macroeconomics

The conventional wisdom about investing is that even after downturns, recovery is inevitable. The advice is therefore to not panic sell, because over any sufficiently long timescale (~decadal) the probability of losing money in a properly diversified portfolio historically is very low. While I am not disagreeing with this premise, I just want to weigh in as a physical scientist: such an argument based on such limited data would not be accepted as scientific fact by scientists. The underlying principle assumes that exponential growth of the US economy is inevitable over the long term, again an assumption that has never been rigorously proven.

The same conventional wisdom will tell you that just because a particular company has achieved X% returns over the past few years, that does not imply that those returns will continue into the future. I am simply suggesting that the same advice could POSSIBLY be relevant to the American economy writ large.

To be clear, I am not cashing out my personal positions. I believe the companies I am personally invested in are resilient enough to withstand the coming storm. This is not investment advice etc. I just have trouble seeing economists and investing professionals declaring certain historical economic trends as laws of nature, when in reality they are much closer to anecdotal evidence by comparison to real scientific experiments imo