Once, a chossid of Rabbi Mendel of Kotzk complained to his Rebbe that he did not remember his learning.
Reb Mendel responded:
“A clear technique for remembering your studies is written in the Torah (Bamidbar 15:39-40), ‘You shall not wander after your hearts and after your eyes after which you are going astray—So that you shall remember.’”
(Sippurei Chassidim, Torah, Pg. 360)