Maslow's hierarchy of needs is a theory that shows a path of psychological development in humans through several hierarchical stages. Each stage characterizes a common set of motivations and needs. The important observation is that a certain motivation belongs to an appropriate stage and in order to occur, all previous stages must be well satisfied. The main goal of the Maslow's theory is to show all prerequisites which a human needs to meet for reaching the top level of psychological development - "self-actualization" - that can be achieved only when all basic and mental needs are fulfilled.
Self-actualization is the need that is perceived very specifically and is described as the desire to accomplish everything that one can, to become the most that one can be, to realize one's full potential. Maslow used this term to describe namely a desire, not a driving force. In his later theory, Maslow also noticed that the fullest realization can be found in giving oneself to something beyond oneself.
For me personally, this theory played an eye-opening role in understanding what was that implicit force which has been pushing me for many years to learn, to immigrate, and finally realize where I'm heading to.