Mussarites claim theirs is a lofty path of slow but steady progress over a lifetime. The experience of any beginner, however, is very different. There is a small but noticeable change between one who has learned or reflected on no Mussar at all and one who has. Immediately thereafter, there is a “Diminishing Law of Returns“, even turning output negative. The immoral Mashgiach (moralist) is a true though common platitude.
As the Chazon Ish explains in his “Emunah Ubitachon”, human beings are not infinitely malleable. And there are no other “factors” at hand. Adding hours and energy to force human change is like pushing on a string (another useful metaphor from the sciences).