Even so, Patroclus, fight disaster off the ships,
fling yourself at the Trojans full force –
before they gut our hulls with leaping fire
and tear away the beloved day of our return.
But take this command to heart – obey it to the end.
So you can win great honor, great glory for me
in the eyes of all the Argive ranks, and they,
they’ll send her back, my lithe and lovely girl,
and top it off with troves of glittering gifts.
Once you have whipped the enemy from the fleet
you must come back, Patroclus. Even if Zeus
the thundering lord of Hera lets you seize your glory,
you must not burn for war against these Trojans,
madmen lusting for battle – not without me –
you will only make my glory that much less.

– Homer

The Iliad, Book 16, lines 92-106. When Achilles lends his armor to Patroclus, he tells tells him that Patroclus can win great honor and glory for him and he will get back his "lithe and lovely girl" Briseis. But Achilles warns him that when he drives the Trojans away from the Greek ships, he must come back, even if Zeus allows him seize this glory. If Patroclus goes on to pursue battle against the Trojans without Achilles, that would make lessen Achilles’s glory, he tells Patrocles. The fact that Achilles is more interested in his own glory than his friend’s safety only serves to demonstrate Achilles’s major character flaw, excessive pride.