If you're going to survive in prison, you have to give the impression of being tough. Even if, deep down, you're not an especially strong person, you have to make the other inmates think that you are. That's why Steve does his crying at night; that way, no one will see his sad face covered in tears. If anyone sees Steve crying during the day, then that will be perceived as a fatal sign of weakness. Steve knows that he could well be spending the rest of his life in prison. That will be a hard enough stretch as it is without being subjected to constant threats of physical and sexual violence. If he's going to get through this ordeal, he has to stay strong. Above else, this means keeping his bitter tears concealed under the cover of darkness.