What does the author mean when he says the man knew in the things they carried?

In Tim O'Brien's "The Things They Carried," when the author says the man "knew," it implies an awareness of the burdens, both physical and emotional, that soldiers bear during and after the Vietnam War. This understanding encompasses the weight of their experiences, memories, and the profound impact of trauma. It signifies a deeper insight into the complexities of courage, guilt, and the human condition within the context of war. Ultimately, it reflects how soldiers carry not just their equipment, but also their fears and regrets.