Why does Athena allow Diomedes to attack Aphrodite?

Athena temporarily gives Diomedes, son of King Tydeus of Argos, unmatched battle prowess. Diomedes battles fiercely, and Athena convinces Ares that they both should stand aside and let the mortals battle it out on their own. The battle is fierce, deaths reported by the speaker, as different Trojans and Greeks fight. Diomedes is hit by one of Pandarus' arrows. His friend Sthenalus tends to the wound, and Diomedes prays for revenge. Athena gives him another wave of strength, as well as a special gift: the mist is lifted from his eyes, and he can now temporarily recognize the gods fighting among the mortals. Athena warns him to face no god head-on, unless it is Aphrodite. Diomedes leaps into battle, slaughtering warrior after warrior.