i found @John_McCall ’s post here to be quite illuminating:
This goal can sometimes come into conflict with the goal of feeling "lightweight", which in many ways comes down to discouraging programmers from brooding endlessly over details that don't really matter. That could certainly happen with access control, if it were too fine-grained.
he was of course, talking about access control modifiers, but i think a similar concept applies to static typing.
i personally think i tend to fall victim to “overtyping”, which i define as encoding too many assumptions into the type system, because well, you can have too much of any good thing. i wonder if this is something that afflicts many swift developers.