"The Red Convertible" is about the bond of brotherhood and how that bond can be severed. When Henry comes back from the war, he is suffering from post-traumatic stress disorder. He is filled with severe anxiety and, unable to deal with the memories of his experience in the war and unable to function in his old life, Henry mentally retreats from his family. Henry alienates himself but only because he doesn't know how to function in his old life. If he can't function in it, he must retreat from that life and everyone he related to. Lyman describes the change in his brother and how even his stillness was plagued with tension in front of the television:
He sat in front of it, watching it, and that was the only time he was completely still. But it was the kind of stillness that you see in a rabbit when it freezes and before it will bolt. He was not easy.
If Henry had gotten psychological help, his chances of dealing with his emotions and living a more normal life would have greatly improved. Since the trauma affected him so badly, Henry saw only one solution and that was suicide; essentially alienating himself from life.