There is a method to learn anything in great depth. It is not fast, it will take time and it will take you deep into the intricacies of the field. In fact, you will become a sort of expert. Here it is, through an analog of understanding a machine.
To learn in detail how a machine works, open it and then reassemble it.
Building the stuff from ground up helps the brain internalize the concepts easily overlooked in learning through other methods by going deeper and making new connections. This is what PhD students all over the world have to do to contribute value to their saturated areas. Let us take a few examples here.
- A car engine: Watching YouTube videos will help but to know better about a car engine, you will have to repair everything yourself. More so, if you actually want to learn its internal mechanisms, you will have to assemble a car engine from scratch.
- Food: Reading delicious recipes is one thing and cooking the food or baking the cake using the ingredients is another.
- Electronics: This is also true for learning electronics. That is why Arduino and Raspberry Pi revolutionized hobbyist electronics in such a remarkable manner.
- Quantum Mechanics: This is also one of the reasons why there are many unknowns in the field of quantum mechanics. We cannot open up, look at and play with the tiniest of the particles inside the heart of a nucleus in an atom. Use this technique to your advantage in countless other areas where there is possible.
As they say, there is a difference between knowing the path and walking the path. The levels to understand anything are not either 0 or 1; there are infinitely many levels in between. And the highest is obtained by the one who dives the deepest into a particular discipline and then resurfaces from the bottom.