When Brian Chevalier was killed in an explosion during a complex ambush, our platoon didn’t take it as an exception to otherwise professional soldiering, or as a mistake that could be corrected on the spot. Chevy’s death was a failure on our part, despite our training, our weapons, and our vigilance. It didn’t matter that the triggerman was hidden from view, or the massive bomb was concealed under concrete. We let him down, and he’s not here because we didn’t keep him safe.