The study of why people's beliefs, attitudes, and behaviors can cause problems with others is a part of:

I believe the answer is Human Relations
Human Relations is often used as the basic knowledge for employees development in modern companies.
It help us analyze employees' behavior, self-development, and help the solve the problem/conflict that they experience in the workplace.

Human relations is defined as the study of why people's beliefs, attitudes, and behaviors can create problems in both personal and professional relationships. Human relations also analyzes human behavior and investigates how to implement strategies that prevent conflict and resolve problems. Self development is integral to successful human relations.