Answer and explanation:
"Condensed Milk" is a short story by Russian author Varlam Shalamov. Shalamov spent fifteen years of his life in a Gulag, a Russian forced-labor camp. "Condensed Milk" is one of the many stories he wrote based on that terrifying experience.
The protagonist and narrator of "Condensed Milk" describes himself as political. That means he was not arrested and taken to the camp for being a regular criminal, a thief. A thief actually received better treatment than he did. He was one of the enemies of the people, arrested for representing some sort of threat to the Stalinist government - maybe he expressed an opinion once that was unacceptable under the Soviet Regime. Even though he is starving, sick due to the lack of vitamins, he is still an intelligent man. When Shestakov offers him a chance to escape, the protagonist won't be fooled. He is living at a time when he knows he can't trust anyone. "Everyone looked out for himself here."
Taking the whole experience of being in a camp and treated worse than an animal would, the protagonist quickly realizes Shestakov is setting a trap. Shestakov is the only one with an office job, with advantages. At that time, having advantages meant being friends with the government, so to speak. "And suddenly I was afraid of Shestakov, the only one of us who was working in the field in which he’d been trained. "Who had set him up here and at what price? Everything here had to be paid for. Either with another man’s blood or another man’s life."
It is this intelligence, this knowledge of governments and people, that saves the protagonist in the end. He demands a can of condensed milk to drink - after, he's been starving -, claiming he needs to recover his strength to run away with the others and Shestakov. After receiving two cans, he tells Shestakov he is not going. And he was right. The five men who did believe Shestakov either ended up dead or with worse sentence after a second trial. However, nothing happened to Shestakov.
Note: Not much is mentioned about the character's cultural background. We have to assume most things. He is most likely an educated man. I believe that and the historical background (Stalinist Russia) are the most important things to understand his behavior.
