When Agamemnon publicly confiscates the captive woman Briseis to replace his own forfeited prize, Achilles, the army's best fighter, withdraws from battle and prays for his own side to suffer. His absence lets the Trojans drive the Greeks back to their ships, and the losses mount until his refusal finally breaks.
A warrior's standing is not internal but is quantified by the public allotment of prizes, so stripping a man of his awarded portion is read as declaring him worthless regardless of his deeds. The insult, not the material loss, is what provokes catastrophic retaliation.
Achilles returns to war not for his commander or cause but because his friend Patroclus is killed wearing his armor, and his private sorrow transmutes into a killing fury aimed at Hector. Anger that once targeted an ally is redirected outward only when loss makes the original grievance feel trivial.
In the final meeting, Achilles looks at Priam begging for Hector's corpse and sees not a foe but his own father's future grief, and the two weep together. Recognizing shared mortality in an enemy can suspend a hatred that no argument or threat could.