It is important to understand before you memorize. It is also related to the 20 rules to structure knowledge, "Rule 1: Do not try to learn things you can not understand."

Recall the parable of the pyramid introduced in Chapter 1. Just by reading books and gathering information, they are just lined up on the ground. You need to accumulate the collected information and create a pyramid.

Psychologists Craik and Tulving did experiments on the relationship between the memory of words and the depth of processing on the words. The depth of processing is four stages, and subjects did one of them for each word. The first stage is "processing of form" that answer the question "Is the word written in uppercase?" For the word TABLE, it is yes. The second stage is "processing of sound" that answer the question "Does this word rhyme with 'weight'?" For the word crate, it is yes. The third stage is "processing of classification" that answer the question "Is the word a kind of fish?" For the word shark, it is yes. The fourth grade is "processing of sentences" that answer the question "Does the word fit in the following sentence: 'He met a ___ in the street.' ?"

After doing those question for a word, Craik and Tulving tested how much subjects remembered the word. As a result, subjects remember only 18% of the words if they processed the form. However, if they did the sound processing, 78% of words are remembered. For the processing of classification, it is 93%. For the processing of the sentences, it is 96%. In other words, you do a more sophisticated process, remember more.

The task of "reading textbooks, finding out what to remember, making it as simple as possible" is sophisticated. You may want to download questions from somewhere or generate it mechanically. However, making questions is the opportunity to do a sophisticated task and make the memory.