The concepts of "good" and "evil" are often explained within a social, spiritual, and ethical context.
For example, "good" behavior is any behavior which complies with an expected conduct that shows kindness, propriety, discipline, and agreeableness. A "good" person is described as someone who has reached a level of awareness of the self and others; such awareness is what motivates the person to behave in a productive and kind manner.
Under the humanistic theory, awareness is the product of having met basic physical, psychological, social, and spiritual needs. According to Maslow's Hierarchy of Needs, the ultimate demonstration of having become a "full human" is by meeting needs that at first essential such as food, water, and shelter. Then, there are security needs, social, esteem, and finally self-actualization needs.
Those needs that are physiological, social, and of esteem and security are called the D-needs. This is because if these needs go unfulfilled, the result is deprivation (D) and this could lead also to irrational and inappropriate behavior. Hence, meeting these needs is essential because they are the individual's immediate self-defense tools from the environment.
After meeting the D-needs, the individual satiates wants and desires that come automatically with development. A safe and healthy development leads to freedom of thought and emotional independence. This is when we seek for our inner self for further growth as a person. These are called B-Needs, or the needs of "being".
These needs of being lead to self-actualization. Once you become self-actualized you also become more aware of what it is to be human and, as such, you become a better person. This is what "good" means under a humanistic perspective.
When the opposite occurs, it is likely that the deprivation that comes as a result of not meeting basic needs will produce frustration, anger, and disillusion. The behaviors that often come as a result of these emotions are antisocial, angry and sometimes even pathological and obsessive. Co-dependence to people or objects, compulsive behaviors, and even deviant conduct could arise as a result of unresolved emotional needs. This is what our society would describe as "evil" or "bad" behavior.
Therefore, good and evil are not discussed under a spiritual point of view. Humanism is about taking the necessary steps to become aware of what it takes to be a productive individual. Something "good" would be the product of taking such steps. Being "evil" would be to detour from everything that is productive, healthy, and socially-appropriate.