Of course same thinking can't easily be applied to things that are not always true, like social behaviour. Part of the reason the replication crisis hit so hard in the social sciences.

And of course this is not really as absolute as I wrote above. No field works like this all the time. But it is a good guideline. If falsifiability is completely ignored, then a concept really is nothing more than a religious belief and should be considered as such.

BTW, Popper did not publish in the 19th century.