When Achilles feels himself insulted by Agamemnon over the allocation of the war prize, he is ambivalent about whether he should kill Agamemnon or restrain his rage:
Grief came upon the son of Peleus, and within his shaggy breast his heart was divided, whether he should draw his sharp sword from beside his thigh, ..., and slay the son of Atreus, or stay his anger and curb his spirit. (Il. 187 ff.)
Once Achilles in Book 1 is persuaded by the gods not to kill Agamemnon and decides instead to sit out the battle, he is conflicted about honour and patriotism. On the one hand, he does not want to see the Greeks actually lose the war, but on the other hand, he does not want to lose face in the conflict over the war prize which is a matter of personal honour. This leads to the compromise of letting Patroclus borrow his armour.