He believed that existence, relationship and growth are three basic factors that individuals need (Clayton, 1969). Unlike Maslow, ERG theory believes that these three needs do not have an inevitable ascending order. When individuals satisfy the need of a lower level, they may go on to chase the need of the next level; when they fail to satisfy the needs of a higher level, they also change to pursue the needs of the lower level; furthermore, once a certain need has been satisfied, the attractiveness of the same need could be further improved. So, unlike Maslow's hierarchy of needs theory, ERG theory emphasizes more on the impact of the individual