The last story was about the one who learns. This one is about the one who teaches. Rabbi Preida had an unusual student.
That student understood only after hearing the same thing four hundred times. So the teacher gave him four hundred, every time.
“Why does it not land today?” “Ever since I heard that you were being called away, my mind has been there.” “Then let us look at it again.” And he taught it four hundred times more. (Babylonian Talmud, Eruvin 54b, translated directly)