A husband may hide the sleeping pills from a depressed wife. A philosophy department may require a student to take logic courses.
A teacher may be less than honest about telling a student that he has little philosophical ability.
All of these rules, policies, and actions may be done for various reasons; may be justified by various considerations. When they are justified solely on the grounds that the person affected would be better off, or would be less harmed, as a result of the rule, policy, etc., and the person in question would prefer not to be treated this way, we have an instance of paternalism.