Repeated practice results in mastery of a skill,or waza.
But even after mastering a waza,one must remain modest and further polish (migaku)one’s skill.
The idea of polishing one’s skills comes from the samurai habit of assiduously polishing a sword to bring out the best.
Training someone in a waza is not just about imparting a single narrow skill.
The teacher’s goal is to make the student a more rounded person in every aspect of life.
(Book:Soul of Japan)