This insight - that modeling human systems is hard because humans also respond to models of their world and then change it - is not all that new, it's called reflexivity [1] and has been around for about the same time as systems thinking.
[1] https://en.wikipedia.org/wiki/Reflexivity_(social_theory)
Also a major contributing factor to second (and third) order effects. Humans, groups, even societies all respond to changes - and if you cannot anticipate what those changes might be, then you are out of luck.
(You will never get all them right. You will never even be able to list what their entirety will be. But you have to be able to predict the order of magnitude of a few of them.)