They teach you everything. If you start with the right book, for example on finding something you enjoy and want to learn more about and teach, you can read a never-ending chain of books teaching you meta-skills, your subject and the skills required to conquer the professional world with it – as well as every other area of life. Continuous self-education through reading is potent. Why does it have to be reading? I don’t know. But I haven’t found any other medium that gives the same depth at the same prize and availability. There’s books on everything, and books about the meta level of acquiring, storing and applying that knowledge. Nobody tries to sell you his product in a book. Instead, you’re given recommendations for more books. By reading for an hour every day, you can gain all the tools you need to improve every sphere of your life. If you expose yourself to enough good literature, you will also adapt the necessary mindsets for applying all your newfound wisdom – the literature will rub off on you. The only times you have to think deeply are when you choose what to read. Start with nonfiction, self-development and classics (e.g. Think and Grow Rich or The 7 Habits of Highly Effective People).