Your working memory quickly forgets newly learned things: you start to forget something new almost immediately, especially in the first 20 minutes. After a few days, you hardly forget anything (of the newly learned material). How quickly you forget something depends on how complicated it is, how tired you are when you learn it, and how important it is to you. How quickly people generally forget something can be seen in the Forgetting Curve of Hermann Ebbinghaus (see image). According to Ebbinghaus, it helps to regularly repeat (you forget it less quickly then), use pictures, and read aloud (you remember it better).
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