The theme of "Condensed Milk" is the complex nature of human relationships and the role that communication plays in maintaining them. The author communicates the message that it is important to be honest and open with those we care about in order to build and maintain strong relationships. For example, the protagonist's strained relationship with his mother is a result of a lack of honest communication, as seen when he hides his job loss from her. Additionally, the relationship between the protagonist and the store clerk is strengthened by their honest conversations about their lives and struggles. These details highlight the importance of communication and honesty in building and maintaining relationships.