If I’m going to spend time learning something, I want it to be as timeless as possible.**
If you want to learn something that’s been proven useful, that’s been tested for dozens of years classic books are best source of knowledge.
Some list of classic books to pick from:
[The 100 greatest non-fiction books] (https://www.theguardian.com/books/2011/jun/14/100-greatest-non-fiction-books)