"really understood" is ambiguous. "solve ___ on a blank piece of paper" is not. Human brains drop unused stuff especially ones that dont fit a known pattern.

"really understood" is ambiguous. "solve ___ on a blank piece of paper" is not. Human brains drop unused stuff especially ones that dont fit a known pattern. No Real understanding without repetition. Repetition breeds memorization. One without the other is fooling yourself either way.