I wrote Ruby with duck-typing for 10 years and it never seemed to be a cognitive load for me. My working memory has been degrading as I age. My Ruby code became increasingly written in a functional style. Maybe it's in how I write? Small functions, minimal (or no) side effects, composed together with names that describe how data is transformed.

Explicating types hinder me. Where it had really started becoming more useful was explicit types in functional programming, such as defining monoids or lattices, or whatever, on those data types. My experience with Typescript and even Crystal is that the static typing only yields a fragment of the benefits without being able to define operators that go with those data types. Even the Just/Maybe monad would have helped with messy external data, since that would explicitly define ambiguous data that can be progressively refined into clean data types.

I'm excited to see the new static typing effort in Elixir. It's theoretical base is a set, which, I think, will work better with how people use Elixir in production. It'll be interesting if the Witchcraft (ML ideas in Elixir) will work with those.