Behavior is a function of both the person and the environment (system). B = f (P/E) Lewin (1936)
There is always a reason why people behave the way they do at work. That reason will always be a combination of things about them (e.g. personality, attitude, values) and things they have little or no control over (e.g. policies, procedures, equipment, staffing, training).
Our explanation for the behavior that we observe (caused by a combination of person and environment factors) is critical because it determines our reaction to the behavior, and the thing we control the most at work is our own personal behavior.