The most frequent error in my opinion is modelling a group of humans as a single human.
I think it's a bit more complicated. I see nothing wrong with modeling a group of humans as a single entity which has, say, particular interests, traditions, incentives, etc. There are big differences between "government" and "politicians in the government" -- an obvious one would be that politicians come and go, but the government (including a very large and very influential class of civil servants) remains.
I am not saying that we should anthropomorphise entities, but treating them just as a group of humans doesn't look right either.
It's a bit more complicated, but still basically true: a group is not very well modeled as an individual. Heck, I'm not sure individual humans have sufficient consistency over time to be well-modeled as an individual. I suspect that (Arrow's Theorem)[https://en.wikipedia.org/wiki/Arrow%27s_impossibility_theorem] applies to subpersonal thinking modules as well as it does whole people.
A single entity which can believe and act simultaneously in contradictory ways is not really a single entity, is it?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.