The scene from Homer's Iliad book 8 where Diomedes rescues a chariot-wrecked Nestor from the advancing Hektor has been accused of being inadequately motivated. Not only is this scene well integrated into book 8, but it has been carefully prepared for in the preceding books. What motivates Homer to incorporate the scene of rescue is the practical consequence of having Zeus impose arbitrary defeat on the Akhaian army. To give the narrative of that defeat minimum dimensions, and appropriate dramatic force, the Akhaians must stage a counteroffensive. However, continuing to fight in the face of direct opposition by Zeus would have seemed both foolhardy and impious. Homer's solution is to adapt a scene from the Aithiopis that can serve to exonerate Diomedes for his failure to retreat in flagrant opposition to Zeus's will. What unifies the scene is the theme of “akhos,” Diomedes' outraged indignation at the seeming arbitrariness of the Akhaian defeat and loss of time, exacerbated by Hektor's boasting speech as Diomedes flees.
University of Chicago Press
Cook, E.F. (2009). On the “importance” of “Iliad” Book 8. Classical Philology, 104(2), 133-161. doi:10.1086/605340