After Joel is taken by the Romans, Daniel determines to rescue him. He discovers that he cannot count on Rosh, who considers people expendable in the larger scheme of the war, and so he gathers a few people together and stages an ambush. Daniel is not stupid, and knows that the rescue is practically guaranteed to be a suicide mission, but he does not want to be the kind of person who sits back and allows his friends to be killed for nothing.
It was no flimsily-guarded caravan they awaited. And behind him was no tight-knit band that would move with precision and cunning, only a cluster of untried boys... Still, he could count on them. He knew that every boy in the band was prepared to give his life. It was up to him, the one they had chosen leader, to see that none of them had to.
(Speare, The Bronze Bow, Google Books)
Daniel has lost Rosh, the man he considered an almost infallible moral compass, because Rosh was willing to let Joel die to preserve the cause. Daniel has now discovered that he is not like Rosh at all; Daniel believes in himself and his men as individuals and as a team, not as pawns to be sacrificed. In the pursuit of his moral obligation to rescue Joel by any means possible, Daniel is willing to sacrifice himself to avoid becoming a coward like Rosh.