Hades had two brothers, Poseidon and Zeus. Each ruled different parts of the universe. Hades ruled the underworld, Poseidon ruled the sea, and Zeus ruled all of the gods, all of Earth, and all of heaven.
Once, Zeus went to visit Hades and Cerberus. Zeus found the ways that Hades ran the underworld unbearable.
Zeus decided to propose some compromises, but no matter what he proposed, he and Hades couldn't come to an agreement.
Zeus shook with anger. As the ruler of all gods, he wanted the underworld to be ran in his way.
As Zeus became more enraged, the sky began to darken and the clouds started spurting bolts of lightning.
This is how lightning happens. When Zeus is mad, dangerous bolts of energy erupt from the sky.