[matheusmoreira]

Standard libraries are very concrete, not academic at all. Learning the standard library means learning how to open a network connection and making an HTTP request to some server. The language becomes useful and gives results immediately. Theory means stuff like language concurrency models, it becomes important once you start considering how to structure the code at a high level. How do I use this language to handle X requests concurrently, hopefully in parallel?

[powersnail]

That highly depends on which language and standard library you are talking about.

Reading C++ standard library gives you headache, and doesn't really teach you how to write C++ in a normal application. For a beginner, this is an impossible approach.

Reading Python standard library means reading C half of the time. Useful for some seasoned Python developers, but not for new comers who want to read Python.

At the end of the day, standard libraries aren't written to teach, and some being a good teacher is a coincident. When you are learning a new language, you really have no idea whether the standard library is a good source for beginners.

I'd suggest a less poetic, more pragmatic approach to learning a new language: ask the most active forum of the language, and use the most common learning materials.