His isolation can’t be broken. He can never come to believe that anybody will ever help him out, ever. If he once thinks there’s an easy way out, he’s wrecked.
As Ender arrives at Battle School, Graff explains to another teacher why he set Ender apart from the rest of the children. By pointing out how advanced Ender appears when compared to the rest of the group, Graff makes the other children jealous and hateful of Ender, a situation that prohibits Ender from making friends. Graff believes that if Ender feels he could rely on anyone, he would not become as good a soldier as could be. Ultimately, Ender’s isolation causes him to suffer greatly throughout the story. Graff, seeming to anticipate Ender’s suffering, justifies the situation by saying that Ender’s isolation will help him become the soldier who will eventually destroy the buggers.
Graff had deliberately set him up to be separate from the other boys, made it impossible for him to be close to them. And he began now to suspect the reasons behind it. It wasn’t to unify the rest of the group—in fact, it was divisive. Graff had isolated Ender to make him struggle. To make him prove, not that he was competent, but that he was far better than everyone else.
After Ender becomes Commander and starts to pick on Bean, Ender wonders why he acts so out of character. He then remembers how, in the past, Graff put him in a similar situation while on his way to Battle School. At the time, he thought Graff’s actions aimed at bringing the rest of the children together, but now Ender recognizes that Graff’s decisions aimed at benefitting Ender alone. For the first time, Ender seems to understand why a soldier must be alone.