As well as biological factors such as hunger, thirst, sexual desire, and basic physiological needs, there also exist psychological forces that drive us. Psychologists Clark Hull (1943) and Walter Cannon (1920) both developed their ideas about the role of these psychological needs in shaping human behavior and eventually came up with a ‘drive reduction theory’. According to them, people act mainly to fulfill their needs and do not necessarily intend to behave in the ways they actually do. For example, eating can be motivated by thirst or hunger, although the person may not consciously know why they are doing what they are doing.
Other psychologists have also noted that humans possess far more than just simple physiologic needs. Human behavior is complex and is influenced by factors such as love, respect, esteem, and achievement. In 1943, Abraham H. Maslow identified a hierarchy relating to these needs, ranging from the need for food, shelter, safety, and security, to the need for self-actualization and personal growth.