I think that the main lesson that comes out of the loneliness that impacts Crooks and Curley's wife is that at the most basic of levels, some need for companionship is required for being in modern consciousness. Crooks has a set up that, on face value, looks appealing. He has his own shed, his own books, and he really is left alone, for the most part. Yet, Crooks' characterization reveals to us that his pain and his hurt lies in the fact that he has no one with whom to share his life. Crooks' envies Lennie and George because of their own companionship and is persuaded to join their plan along with Candy because of the desire to be with other people. There is an isolation that impacts Crooks' being and while he protests that he is find being on his own, the ointment that he rubs on his shoulder at the start and the end of the fourth chapter might be symbolic of the pain that eats away at him caused by his isolating condition. This isolation or alienation is something that Steinbeck continues in his depiction of Curley's wife. While she is admired by so many and seems to never be of want for company, as opposed to Crooks, she is internally lonely. Her desire to want to be in "pitchers" reflects how sad she fundamentally feels about her own condition in life, one in which emotional intimacy is impossible. Her pain resides in being unable to emotionally connect with anyone, something that is almost accomplished in her dialogue with Lennie. In her death, there is a sad statement about how she was willing to "die" for someone to talk to. Steinbeck is suggesting in both characters that loneliness and isolation from human beings is the fundamental pain that lies at the heart of the modern predicament. Emotional and social solidarity with others is the only way to avoid such a condition and reflects a way that being should be as opposed to what is.
Although Curley'swife is lonely, her loneliness lies in the fact that she has much to give but her physical looks are the only thing that people are desiring. She is willing to talk but not many are willing to listen. Steinbeck often shows this through his depiction of his strong character portrayals. crooks controls his life through his neatness. This again gets him nowhere. People are incapable to connect especially in the world of migrant workers of the time. This time period was more of existing and people looked past the need for valuing and connecting with others. Struggles were often lonely and when people did connect it became a lesson that steinbeck brought out as important to the human Base condition.