Why does Ishmael start to believe the phrase, "none of these things are your fault"?

In the UNICEF compound, Beah finally begins to trust someone. He had learned through hard experience that circumstances would collaborate to cause him harm; even in the military, where he learned comradeship through blood spilled, Beah found that he could be betrayed: “People like the lieutenant, whom I had obeyed and trusted, had made me question trusting anyone, especially adults” (p. 153). When even a man who held others’ lives in his hands could turn traitor (by sending Beah with the UNICEF workers), there was no one left in Beah’s world to confide in. He has learned that “people befriended only to exploit one another” (p. 153). Beah finally understood that none of what happened to him was his fault.