He is motivated by his need to fit into the role of being a family man.
However, once Gregor is inexplicably transformed into an Ungeziefer— which is roughly equivalent to “vermin”— he is no longer capable of taking care of his family in a traditional capacity. Instead, he is relegated to being a blind, wilting creature. All of his energy goes towards looking out the window, even as his vision and perception deteriorate.
He devolves from desiring to care for his family and retain his job to desiring nothing more than to delude himself into believing that his sister is playing the violin for him. He scurries out into their midst, no longer conscious as his familys need for him to remain hidden. He confronts his mother with his shriveled form and terrifies their lodgers with his uncleanliness.
Ultimately, Gergors nature as a man is completely destroyed. As his family —however horrid they might be— points out, “If [this creature] were Gregor he would have seen long ago that its not possible for human beings to live with an animal like that and he would have gone of his own free will.” Gregor has lost his ability to place his family above himself, but he still retains his ability to feel affection as evidenced by the “emotion and love” he holds for his family. The obligation that he held as a traveling salesman, however, has long since faded away, taking with it the satisfactions and desires that mark him as