In the novel, Crime and Punishment, by Feodor Dostoevsky, Marmeladov asks Raskolnikov "Do you understand, sir, do you understand what it means when you have absolutely no one to love?" The idea of man being all alone becomes a major recurring theme in the story. In the novel, isolation is the cause and effect of the murder as well as the cause and effect of the punishment.
The novel begins with Raskolnikov intentionally isolating himself. He, on purpose, separates himself from all human society. This allows him to detach himself from all humanity and the feelings of love and compassion that belongs to it. Therefore, he can think of concepts in a purely philosophical frame of mind without any humane distractions. Without taking human feelings into account he could then proclaim that extraordinary men have the right to commit any crime if they think it's proper at the time. Also, his definition of an extraordinary man is anyone who could invent a "new word". Since his deriving this whole idea is something new, he gave himself permission to commit the murder in his own mind.
After Roskolnikov commits the murder, isolation becomes an after effect of the crime. Even in his own philosophy Roskolnikov believed that crime isolates a person from society. If one wants to get away with a crime without being punished one is forced into isolation. A criminal cannot trust anyone with their secret because there is no telling if someone might reveal your secret to the public. This exactly what happens with Roskolnikov.
Towards the end of the novel Roskolnikov admits to the murder for the purpose of returning to society. The only way he could end his isolation was the revelation of his crime. Once his crime was out in the open he was no longer completely isolated from society. He finally had someone he could talk to.
The punishment for his crime is clearly another form of isolation. He was punished to jail in Siberia. However, he still had one companion from society: the person he admitted to, Sonia. In the epilogue, Rokolnikov realizes that once the physical isolation of jail is over, he has many years of joy left with Sonia, the person who brought him back into society.