The learning is often sufficient to serve the needs at the moment. If I have to quickly fix my juicer, I don't under go do Electrical and mechanical engineering courses for the next 4 years.
Instead what I do is, I define the problem. Search for the solutions on the internet. The solution requires me to understand some theory and some practical aspects of things with some tool usage. It is more than sufficient to that to solve the problem for the moment.
That is how most of the software is, its practically impossible to know every thing from the book. What is more important today is given the body of knowledge can a person study and solve the problems. A person can be productive and deliver the goods with the above approach, With a little discipline.
That's how most knowledge based work happens in the 21st century.
I also see a lot of people around me trading stocks, although they understand virtually nothing about economics in detail. For the most the part they can make 10-15% profit on their investment by just using some basic analytical skills.