Earlier quoted context omitted.
They are usually not hidden, so they are at least easier to identify.
This is the crux of the matter. Every paradigm is argued about using small program examples, but the real-world issues come as the codebases become large (1M LOC or so). Then the cracks become worriesome. Imperative non-OO codebases become swamps of maybe (hopefully?) layered code, where each layer contains its own sinkholes and completely bizarre structure (or lack thereof). It's basically a bunch of mini-codebases…
OTOH isn't that just - you need to know what the function you are calling is doing and how, and read the doc. Whereas in imperative you would implement it yourself, with the pitfalls of that.
If you are coding in Python and you are using a lot of numpy you need to know how to feed data in, how to get data out, etc. so maybe FP programming should treat the STD-lib more like an external library because the building blocks are a bit more high-level?