I agree on the distinction between internal vs. external complexity; this particularly resonates with me: "the Go runtime is relatively complex internally but it permits simple APIs and programming models for users...". I probably should've made it clear that the external interface of a system (whether it's a UI or an API) should be simple and abstracts away the internal complexity.
To go back to the human body analogy, while the internals of the human body are complex, the external interface is extremely simple: you eat to get energy; you sleep to get rest; you use your reproductive organs to reproduce; etc. You don't have to learn how the internal systems work to operate your body.
To go back to the human body analogy, while the internals of the human body are complex, the external interface is extremely simple: you eat to get energy; you sleep to get rest; you use your reproductive organs to reproduce; etc. You don't have to learn how the internal systems work to operate your body.