Conversely, I do like to talk about the concrete ways that things can go wrong — I think it’s helpful for people to understand not just how things are in the abstract, but also why things are that way. It’s the same way I like my mathematical definitions and proofs: accompanied with a bunch of examples to motivate why someone thought up the abstraction in the first place 
Speaking of how things are in the abstract, has anybody tried to write down an abstract machine model for Julia? I guess not, but presumably we’re quite similar to abstract machines for existing languages. Could we roughly document the Julia abstract machine by analogy to one which already exists? Which one?