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In Kafka's The Metamorphosis, Gregor begins to go through a second transformation or metamorphosis, and this is based completely upon how his family treats him.
When Gregor went out to work and supported the rest of the family, no one had any complaints. They were satisfied (though seemingly not grateful) that he paid the bills which allowed Gregor's sister and parents to live at home comfortably—and unemployed. However, when it becomes impossible for Gregor to go to work when he is turned into a giant insect (and it really is the only thing that stops him...because he tries for some time after he wakes to figure out how he can catch the train...), the family starts to look at Gregor very differently.
At first, Grete tries to find foods that he will eat and shows some concern for her brother. After a while, however, this changes. Grete becomes empowered by her brother's tragic circumstances. Ultimately, she stops cleaning in his room and even puts odd furniture and junk in there, which greatly upsets Gregor. This is the beginning of Gregor's demise. Gregor is not allowed out of his room. In fact, the one time he comes out and scares his mother, Grete throws accusations about her brother's behavior before their father, and he throws apples at Gregor, seriously wounding him:
He had filled his pockets from the fruit bowl on the credenza, and now, without aiming precisely, threw apple after apple...One direct hit that flew immediately afterward penetrated Gregor's back; Gregor wanted to drag himself a little further, as if the unexpected and unbelievable pain would go away with a change of position, and yet he felt like he was nailed down and stretched out...
The apple remains lodged in his back for the remainder of Gregor's life. The lack of support from his father and sister is devastating to Gregor. And as much as his mother would like to be supportive of him, she is unable to handle what he has become—she suffers from ill-health and seeming overwrought nerves. However, the moment when Gregor gives up his struggle to survive arrives when his sister (who once dearly loved him) betrays him to the father and mother, insisting that he must go. They have all become independent; they have realized in Gregor's "illness" what they never chose to see when he was well: that had always been capable of helping so Gregor might not have had to work so hard. Now they don't need him at all. In Chapter Three, Grete says:
“Dearest parents...this can go no further... I will not pronounce the name of my brother in the presence of this monster...we must be rid of it. We have attempted every method humanly possible to serve and tolerate it...He must be sent away, that is the only way. You just have to try to banish the thought that it's Gregor. ”
For Gregor, there is nothing to live for—no hope. He returns, without being tormented, to his room. As he slowly enters, Grete runs to slam and lock the door in triumph.
“And now?” Gregor asked himself as he looked around in the darkness. He soon made the discovery that he could no longer even budge.
In pain, and lacking all energy, Gregor fades and dies early in the morning. No reason for his death is ever given, but one can assume his heart has been broken—at the hands of his family.