One of the most important Greek gods was Demeter, the goddess of the harvest. Everyone wanted to keep her happy because if she wasn't happy, the crops wouldn't grow, the people would starve, and the gods wouldn't have anyone to mess with in their spare time.
Fortunately, Demeter was happy most of the time because of her daughter, Persephone, so the crops kept growing all the time.
One day, Hades, the king of the Underworld, came outside on a stroll with his dog. When he saw that Persephone wasn't afraid of the dog, he fell in love with her and decided to do what any normal god of the Underworld would do: kidnap Persephone and take her to his home.
In the Underworld, Hades attempted to give Persephone some fruits, but she wouldn't eat any because she heard that if you ate food from the underworld, you would stay there forever. Unfortunately, she ate some pomegranate seeds because she became R E A L L Y hungry after seven days of not eating anything.
Meanwhile, the crops were failing because Demeter was in depressed mode. The gods decided to do something about this, so they asked Hades if Persephone married him, he would let her six months in the Overworld, and then she would stay six months in the
Nether Underworld with him.
So, that is the tall, alcohol-induced tale of how we got the seasons. During the six months, we have Spring and Summer, when crops are grown and harvested, and during the other six, we have Autumn and Winter, when no crops grow. EXCEPT IN TROPICAL CLIMATES!!! (The ancients didn't really think about that.)