experiences as a soldier.Lieutenant Jimmy Cross is the main character of the title story.

Cross is a young soldier, drafted like many others, and committed to the war effort and getting his men out alive. He is not emotionally or patriotically committed, instead simply seeing the war as his assigned job to which he gives his best effort. Initially, before the death of Ted Lavender, Cross is distracted from the day-to-day war by his feelings for a girl back home, Martha; her letters and photos are a fantasy for him:

He remembered kissing her good night at the dorm door. Right then, he thought, he should've done something brave. He should've carried her up the stairs to her room and tied her to the bed and touched that left knee all night long. He should've risked it. Whenever he looked at the photographs, he thought of new things he should've done.

In his head, Martha is a beacon of regret, symbolizing all the things he feels he should have done while he had the chance; Cross knows he might not get the chance later. As the war drags on and Cross loses his innocence, he gives the fantasy up:

He was realistic about it. There was that new hardness in his stomach. He loved her but he hated her.
No more fantasies, he told himself.
Henceforth, when he thought about Martha, it would be only to think that she belonged elsewhere. He would shut down the daydreams. This was not Mount Sebastian, it was another world, where there were no pretty poems or midterm exams, a place where men died because of carelessness and gross stupidity.

By divesting himself of the fantasy world, Cross becomes a better leader of his men; this is his only goal now in the war, since he feels that his men do not deserve to die but he cannot take their place.

Jimmy Cross did not want the responsibility of leading these men. He had never wanted it. In his sophomore year at Mount Sebastian College he had signed up for the Reserve Officer Training Corps without much thought... He was unprepared. Twenty-four years old and his heart wasn't in it. Military matters meant nothing to him. He did not care one way or the other about the war, and he had no desire to command....
(All Quotes: O'Brien, The Things They Carried, Google Books)

Cross feels responsible for their lives, but not for his own; he is committed to the war only in that it is a job. His guilt allows him to shoot his own foot, taking him out of the war, and when he returns home, it is hard for him to relate to others because of the mental damage from the war. Today, Cross would be seen as a typical victim of Post Traumatic Stress Disorder, and a standard "type" of Vietnam soldier: the drafted young man who is forever changed and damaged by the war.

Jimmy Cross, the leader of a squadron of American soldiers in the Vietnam War, faces a conflict between his desire for Martha, a woman at home, and the immediacy of his leadership duties in the war. Eventually, Cross feels that the distraction caused by his obsession with Martha leads to the death of one of his men, Ted Lavender, which makes him rethink his priorities and dedicate himself to his men.

Jimmy Cross is the protagonist of Tim O'Brien's "The Things They Carried," the first story in a collection of the same name. Cross carries letters from a woman named Martha, with whom he seems to have had a casual friendship before the war. In his memories of her, it seems that she is not interested in a romantic relationship with him but does maintain a correspondence with Jimmy during the war. He occupies himself at war by thinking of her and reading her letters. Martha provides an (arguably necessary) escape from the harsh reality of war. Each solider in Cross's unit has a similar way of relieving stress and tension from their everyday reality. However, when Ted Lavender is killed on the way back from relieving himself one day, Cross takes responsibility for the death, feeling that he had been too distracted and let conditions in his camp become too lax. Cross commits to being a stronger leader, more strict and less laid-back, and he burns the letters from Martha as a symbolic gesture of that commitment.

The ending of "The Things They Carried" subtly suggests that Cross may be wrong when he resolves his conflict in this way. He must give up his humanity. The narrator explains,

He would show strength, distancing himself.

Among the men there would be grumbling, of course, and maybe worse, because their days would seem longer and their loads heavier, but Lieutenant Jimmy Cross reminded himself that his obligation was not to be loved but to lead. He would dispense with love; it was not now a factor ... Or he might not.

The final paragraphs of the story indicate that if Jimmy were to become stricter, the men would have more to carry. He would "distanc[e] himself" by focusing on "leading." There would be no need for human connection or emotion. This seems like a criticism on O'Brien's part of the way war dehumanizes soldiers. But then again, Cross may not change. He may find that being stricter does not work and may be able to hold on to some of what makes him human.

It seems obvious that by far the biggest conflict that Jimmy Cross experiences is not the obvious physical external conflict that surrounds him through the war, but actually the internal conflict that goes on inside of him and his tendency to engage in daydreams concerning Martha, even though he knows that she is not really interested in him. He blames these daydreams for the death of Lavender, as it was when he was engaged in one of these daydreams that Lavender was shot. Note how this conflict is resolved at the end of this story when Jimmy Cross burns Martha's photos and letters:

He was realistic about it. There was that new hardness in his stomach. He loved her but he hated her.
No more fantasies, he told himself.

He from this point onwards determines to only think of Martha as a figure that "belonged elsewhere" in a very different world of "pretty poems or midterm exams." He inhabits a world where men died because of "carelessness and gross stupidity," as the death of Lavender has shown, where daydreams were a dangerous luxury that could have serious consequences. Thus he will "shut them down." The sadness and conflict however, is that the horrors and grim realities of war are that much easier to bear if one does have daydreams to turn to, and we fear for the new "hardened" Jimmy Cross who deliberately eschews such release.

Lt. Jimmy Cross is an idealistic man. His draught to war signifies more to him than just a task: He believes that he is somehow selected to perform a duty that is almost otherworldly.

When he becomes "a soldier", Jimmy takes on the role with somewhat of a knightly disposition. For example, he idealizes Martha as some sort of damsel in distress who yearns for him and writes him letters of love.

He imagined bare feet. Martha was a poet, with the poet's sensibilities, and her feet would be brown and bare the toenails unpainted, the eyes chilly and somber like the ocean in March, and though it was painful, he wondered who had been with her that afternoon. He imagined a pair of shadows moving along the strip of sand where things came together but also separated. It was phantom jealousy, he knew, but he couldn't help himself. He loved her so much.

He also feels that he is responsible for the death of Lavender, for the choices that other soldiers make, and for the outcomes of his platoon. Surely he is partially responsible for his men, but only in the capacity of a military officer, not because he has any kind of divine assignment in the lives of the other men.

However, the point that O'Brien wants to make in "The Things They Carried" is that Jimmy's attitude is not uncommon for many men to assume during circumstances like that. A man who suddenly becomes a soldier is given responsibilities and tasks that he has never performed before. Additionally, he is made aware of his important role in the lives of men that are as scared and shocked as he is.

The fact that Jimmy is more educated seems to allow him to make the experience all the more theatrical in his mind. Even if men know things for what they really are, they are prone to make much more of it in a stressful situation. Although Jimmy carries Martha's letters around and uses them as a devotional object, the facts still remained:

The letters weighed ten ounces. They were signed "Love, Martha," but Lieutenant Cross understood that Love was only a way of signing and did not mean what he sometimes pretended it meant.

In the end, Jimmy realizes the importance of valuing reality. As death gets closer and closer to the platoon, Jimmy slowly understands that life has to be taken for what it is. No gimmicks, no sad stories: He has a task that he must complete. Hence, the way he changes is by finally accepting that reality may not be as fun as fantasy but, in the end, holding strongly to it will be what ultimate saves their lives.

Here is a topic sentence with the three claims enumerated in parentheses:

Like so many young officers sent to Vietnam, twenty-four year-old Lt. Jimmy Cross is (1)as confused and overwhelmed by the ambiguities of the foreign conflict in which he finds himself as the young men under him; in this confusion, (2) he seeks escape from military objectives and engages in reveries of Martha, a girl he loves from home, but after the death of Ted Lavender, a death about which he feels responsible, (3) Cross vows to lead his men with the new "hardness in his stomach."

In the beginning of "Things They Carried," there is a sense of nomadic wandering by the men, who carry the trivial and the dangerous necessities of war on their persons. Lt. Jimmy Cross appears to be as ambiguous of purpose as the "grunts." For, he must shake himself out of his fantasies about Martha and look at maps and position his troop, although he quickly returns to his romantic fantasizing and "he was not there." Even when the men approach the tunnel, Cross envisions himself with Martha in this tunnel. However, when the realities of war come despite his carrying of his good luck pebble from Martha, Lt. Cross trembles with the horrible reality of Ted Lavender's death. It is then that he feels "[A] dullness of desire and intellect and conscience and hope and human sensibility." So, he burns Martha's pictures and letters, he cannot "burn the blame" as he feels responsible for the loss of Lavender. Now, Cross knows that 

their calculations were biological. They had no sense of strategy or mission....They carried their own lives. The pressures were enormous.

Feeling responsible for the death of Lavender, the lieutenant vows to be vigilant and sterner henceforth. In his interior monologue, Cross promises himself to assume "the correct command posture."  With a new "hardness in his stomach," Cross vows to keep the men under his control and be the officer he should be. He leads his men to a village where they kill and destroy, but he cannot assuage his guilt.