What can be harmful when applied to students?

Holding grudges can be harmful when applied to students because it creates a negative atmosphere that can hinder their learning and development. In an educational environment, it's crucial that instructors maintain a professional and supportive demeanor. If an instructor harbors resentment or negativity toward a student, it can lead to feelings of alienation and discourage the student from engaging fully in the learning process. This can affect the student's confidence, motivation, and overall experience in the classroom.

By being unable to let go of past issues, an instructor can inadvertently undermine the trust and respect essential for a healthy teacher-student relationship. This might lead to a lack of open communication, where students feel less comfortable approaching the instructor for help or guidance. Thus, addressing past grievances and maintaining a positive, constructive relationship is vital for fostering a productive learning environment.

Although the other options may also have negative impacts, they do not involve the personal emotional baggage that can interfere directly with an instructor's ability to teach effectively and impartially.