I often hear people say that theory is waste of time. Reading books is a waste of time. Theory alone is indeed a waste of time, unless the person is looking to learn for the sake of curiosity (which in itself is interesting). But the reality is, people without fundamental knowledge will spend a lot of their lifetime re-inventing the wheel.
There are two distinct ways to improve in any craft, namely learning from one's own experience or learning from an expert. The latter is the most effective choice as you learn to focus on the most efficient strategies and avoid expensive mistakes. By yourself, you simply have to go through all the experiences which will take a lot of time and money.
One cheap yet valuable way of learning from experts is by reading books. You get relevant knowledge at the fraction of the price you would have by booking him or her.
As humans, we mostly learn by trial and error. We experiment with different methods and strategies in order to get quickest results. Heuristics are mental shortcuts or maps we develop through experience to help us make decisions and solve problems.
You need hundreds of hours of experience in order to become excellent in your field. At first, you need to understand the fundamentals. You then need to work on your blind spots and develop the relevant skills. Once you've mastered the subjects, you develop mental shortcuts or heuristics, of all which takes years.
One such popular example are footballers. Most of them start training at the age of five or six but start playing professionally almost a decade later while undergoing tough training several times per week.
Reading books and seeking the basic theory brings another factor: motivation.
A few years back, I watched a single video about 50 minutes long on a new technology at that time, whereby the author explained his decision behinds and how he crafted it.
This alone convinced me to try the technology and move company to work on it. Since then, the framework, AngularJS has been a major success, spurning rivals such VueJS and ReactJS.
A recent life scenario
Hearing about the success of SvelteJS, a technology similar to Angular, Vue and React but being mostly a compiler instead of a framework - I try using it directly - without first reading the documentation and understanding the basic theory behind.
In my mind, this technology is similar to the above frameworks (library in the case of ReactJS), which I have years of experience working on. I therefore assume I can start working on directly skipping the getting started documentation and beginner's tutorials.
I however struggle with the syntax - let alone the concepts - even though it's similar to VueJS. I shall therefore follow the introductory documentation and watch a few hours of video tutorials on Youtube.
This is how I learned and became productive on Angular, ReactJS, VueJS and Ruby on Rails. I even followed courses on Udemy so that I feel comfortable with the overall concepts to jump in.
Reading and Applying
I am working right now on one of my weaknesses - which is negotiating skills - by reading bestselling books on the subject.
I am also, however, practically applying lessons learnt by talking to a maximum of person I can.