Abraham Maslow proposed a hierarchy of needs consisting of physiological needs, safety needs, love and belongingness needs, esteem needs, and self-actualization needs. He believed humans are motivated to fulfill deficit needs but also have a drive for personal growth. Maslow's hierarchy describes how lower level needs must be satisfied before higher level growth needs can be pursued. Self-actualization, achieving one's full potential, is difficult as safety needs can discourage risk-taking needed for growth. Maslow studied self-actualized individuals like Einstein to understand characteristics like peak experiences.