[3cats-in-a-coat]

Black box systems imply "here's the box, it has input and it has output, use that to understand it without opening it". Social networks are not like that. You don't have all the inputs nor all the outputs. You have a tiny sample of both, on a live system that constantly receives input and produces output, in a feedback loop too, and virtually no way to verify your sample is not a biased sample.

In that sense, a black box system is trivial in comparison to something as big as a social network used by hundreds of millions or billions of people.

Social networks, due to their nature also have "eventual consistency" meaning it's unclear when something should occur (and if it'll ever occur) as an effect of a cause. And it also has probabilistic behavior, where things happen sometimes, depending on which server you hit, with what state, what version of the software, and internally it literally does things with a PRNG often (it samples its own input), so there's that as well.