Insufficient teaching ability
Some teachers lack the necessary teaching ability. Such teachers may not have received a good education, lack teaching experience, and do not know how to design appropriate courses and activities, let alone how to solve the problems raised by students.
Lack of educational enthusiasm
Some teachers may lack enthusiasm for education. These teachers may feel tired, depressed or dissatisfied with their work. This shows that they don't really care about students, and they don't take the initiative to help them.
Lack of professional ethics
Some teachers may lack professional ethics. They may be partial to some students, unfair to some students, or take immoral actions to achieve their goals.