However, we can infer some reasons based on the context:
* Their shared respect for wisdom and power: Although their personalities clash, both Poseidon and Athena are powerful Olympians with a strong sense of justice and wisdom. They likely respect each other's strengths and contributions to the Olympian council.
* Their children's relationship: Annabeth mentions that the children of Athena and Poseidon (the demigods) often get along well, perhaps because of their shared understanding of their unique circumstances. This could indicate a level of understanding and cooperation between the parents themselves.
* A truce for the sake of Olympus: It's possible that, despite their personal differences, Poseidon and Athena recognize the need to maintain a semblance of peace within the Olympian hierarchy for the sake of the world and its demigod population.
While Annabeth doesn't explicitly explain their relationship, it's implied to be a complex one with a mixture of respect, rivalry, and perhaps even a touch of begrudging cooperation. Remember, the Olympian gods are not known for their harmonious relationships!