There is no "can't" in martial arts. It is perfectly all right for students to state that they are "still working on it", "have not mastered it yet", or "are trying as best they can" as all of those sentiments reflect willingness and perseverance. It is not all right, on the other hand, to verbally or physically portray reluctance, vacillation, or defect.
Lawrence Kane
martial-arts, perseverance