
The Greeks made their gods powerful, but they didn't need them to be infallible. The Olympians were more like people; they had pride which could be swelled or injured, love, hatred, jealousy, sexual appetites, creative instincts and, every once in a while, they'd strike a deal.
One of the most famous of these deals (well, if you're a classical mythology geek) is the story of Hades falling in love with Persephone and opening the Earth to swallow her so she could be his queen in the underworld.