This is a very interesting question. To me, understanding in isolation some random function deep down in the code somewhere is not really something I do. Maybe that's why I prefer dynamic languages. And other people like to be able to do that, and therefore prefers static languages.
This has definitely been a challenge for me in Clojure when trying to use a library that isn't well-documented. Using the REPL helps because I can throw random things at it quickly, but it's still very frustrating.
An interesting corollary to this problem though is the wandering type-path, where when consuming (again, poorly documented) a Java library, I know the type of the function I want to call, but not how to get that type. Usually it's:
"I have B value [byte-array, int, whatever] and I need Z from this library so I can call `Z.foo`... Z's constructor takes Y, which takes X, which takes..."
Types help there, but they also hinder quite a bit if I have the correct underlying data type, but can't get Java to accept it.
