the answer is: Unlike Maslow's theory, the ERG model suggests that individuals may move down as well as up the needs hierarchy, depending on their ability to satisfy needs.
Maslow's hierarchy of needs describes an evolution of needs that can be undone, starting from basic needs and climbing up to the top when people develop a need for self-actualization.
ERG suggested that the progression of needs could be undone depending on people's situation.
For example, let's say that Tina is born into a rich family. All her life she does not have to think about basic needs because it will be provided by her parents, so she can shoot directly to needs in a higher hierarchy (such as self-actualization).
But, a misfortune comes to her family and they suddenly become poor. In this situation, Tina's could move down to the lower hierarchy of needs and focus on her life to fulfill her basic needs rather than self-actualization.