YouTube Video, Sprouts, 2017 by Barbara Oakley: "According to learning expert Dr. Oakley it can hold only 4 chunks of information at once. So when new inputs arrive it has two ways to pick them up. First, it can overwrite and forget what it has to make space for new information. Or it can use mental effort to move a chunk from the working memory into the long-term memory where it can be stored and remembered later.

This is why its almost impossible to recall 9 digits like 081127882. There is simply not enough space. Once chunked, there is.