I'd say this is generally true, but in practice there are a decent number of cases where some reasoning can give you a pretty good confidence one way or another. Mainly by considering what other correlations exist and what causal relationships are plausible (because not all of them are).
(I say this coming from an engineering context, where e.g. you can pretty confidently say that your sensor isn't affecting the weather but vice-versa is plausible)
This is true fundamentally. It is not general. It is a fundamental facet of reality.
In practice it’s hard to determine causality so people make assumptions. Most conclusions are like that. I said this in the original post that conclusions from observation alone must have assumptions made. Which is fine given available resources. If you find people who smoke weed have lower iq you can come to the conclusion that weed causes iq to lower assuming that all smokers of weed had average iq before smoking and this is fine.
I’m sure you’ve seen many causative conclusions redacted because of incorrect assumptions so it is in general a very unreliable method.
And that’s why in medicine they strictly have to do causative based testing because they can’t afford to have a conclusion based off of an incorrect assumption.
Sorry, I meant in general in the broader sense that you were intending (i.e., I agree). And if you really get down to brass tacks, it's not obvious you can actually do truly causative based tasting. (See e.g. superdeterminism, which posits that you fundamentally can't as a way to explain quantum weirdness in physics).
(I say this coming from an engineering context, where e.g. you can pretty confidently say that your sensor isn't affecting the weather but vice-versa is plausible)