Mac is not educated like Jim is. The two men have many differences and this is one of them. It is not well-read, but he has significant experience working for the communist party in various capacities. He writes letters, trains new members, and organizes strikes.
Mac says that he has been involved in a number of strikes and has experience dealing with mobs of strikers and mobs of police. He also is familiar with the behavior of vigilantes.
Mac's experience and his close attention to people's motivations and behavior combine to give him some special insights. However, even Mac is unable to predict many decisions that the strikers make.