What it is
The Feynman technique can be summarized as, "the best way to learn is to teach." This technique involves taking a particular topic and teaching it to someone else, using as simple language as you can while still accurately conveying the topic.
How to do it
This is not a recitation of a rote memorized passage. It has to be an explanation formed from your own words. Pick any willing listener, or unwilling, or a chair, and simply explain the topic to them using simple language. Try to convey all of the nuance and intricacy of the topic, but do so as clearly and concisely as possible. When you struggle to put a certain aspect into your own words, or when your listener asks a clarifying question you can't immediately answer with simple language, or when you encounter a complex point that you can't articulate simply, make note of it. These stumbling points are areas where your understanding is less clear, and they should guide your study sessions so you can make the best use of your study time.
Repeat the process until you can articulate the entire topic simply and concisely.
When to apply it
Any time you are learning new material (combine with QFT and SQ3R) or reviewing old material (goes great with Recall vs Recognition). Teaching the topic to a chair is similar to the Awkward selfies technique, though communicating to a live person is typically more productive.
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