Maslow's hierarchy of needs is a theory in psychology that human motivation is based on a five-tier model of physiological needs, safety needs, love and belonging needs, esteem needs, and self-actualization needs. The lowest level needs must be met before progressing to meet higher level needs. Self-actualization is achieving one's full potential and is considered the highest level of human motivation and development. Effective leaders address the needs of their followers and are able to adapt to changing needs over time by progressing up the hierarchy themselves.