In the last quarter of 2018, I came across a post about learning things better. Some of the points made were different - be sure you are well hydrated and have enough sleep. The post also mentioned a book called "Make it Stick" which I purchased.
I am still in the process of reading the book, but one of the key points so far is the idea of making sure you recall the information repeatedly. The book gives multiple examples of how testing on knowledge repeatedly shortly after learning, make the information retention much more successful. Pop-quiz is actually helping to ingrain the information for better recall.
Taking classes in anything, and then not using it - create a use-it-or lose it situation. Learning something, as you are about to use that knowledge makes that much more permanent. So doing the exercises from a chapter in a book- helps retain the info - even better is making your own exercises for the information.
I have recited the phrase "you have to teach in order to learn" - educators refer to this is "Learn by teaching" where the students learn material they must teach others with. This causes you to refine the information you have learned, putting into your own words and being able to express your understanding to others - independent of the material.
Learn by doing - is what exercises are for - it forces that retrieval of information - whether it is technical in nature, a musical instrument, or in cooking. You learn it better when you retrieve that information and apply it; then it penetrates more deeply.
I have read in some of my chess books, you have to play a lot of chess - where you apply what you have learned, and see how it works out. One story from the 18th century had a person learn the basic moves, and in the course of the day, learned enough that they were able to win a game at the end - they were so enthusiastic they went and read chess material and playing out the moves on a board - doing almost nothing else (not eating or drinking) - and when they returned to play against another person they lost repeatedly. They had read a great deal and had a lot of theory - but they needed to actually apply that information repeatedly so that the patterns of how things worked penetrated; they needed to be able to use that knowledge independent of the material.