On a certain day in the Hindu calendar, which usually falls in October, you are not supposed to look at the moon for the entire night. If you do look at the moon you will receive bad blessings. The only way to get rid of these bad blessings is to if another person tells you the mythological story of why not to look at the moon.
In Hindu mythology there is a story of a god who one day ate too much. He ate so much that he fell off of his vehicle. When he fell the moon started to laugh and make fun of the god. Then the god cursed the moon saying that no one will look at the moons face. So on that day, the day the moon laughed at a god, no one is supposed to look at the moon. But if they do, they will receive bad blessings.
Upon hearing this story I decided to look further into the specifics and found another, very similar version of this mythology in Hindu Feasts and Festivals by Sri Swami Sivanadanda. In this version, Lord Ganesha is the god mentioned. He is an embodiment of wisdom and bliss and has a small mouse as his vehicle. Ganesa is the first god, he has the head of an elephant- the biggest of all animals- and rides on a mouse- the smallest of all animals. This denotes that Ganesha is the creator of all creatures (Sivanadanda 43).
On his birthday Ganesha was going to different houses accepting offerings of sweet puddings, which he loved. After eating a lot of pudding he set out on his mouse at night. Suddenly the mouse stumbled because it saw a snake and Ganesha fell off. Ganeshas stomach burst open and all of the sweets spilled out. Ganesha stuffed the sweets back into his stomach and used tied the snake around his belly. The moon and sky laughed after witnessing this. Annoyed, Ganesh pulled out one of his tusks and hurled it against the moon and cursed that no one should look at the moon on the Ganesh Chaturthi day or else they will earn a bad name. If someone does look at the moon by mistake then the only way he can be freed rom the curse is by repeating or listening to a different story of how Lord Krishna cleared his character regarding the Symantaka jewel. (Sivanadanda 44)
This story also has central ties to the Hindu doctrine of Karma, essentially what goes around comes around. In this case, if you laugh at a high god, you will be cursed. This story also serves to teach respect for the spiritual superiors despite mistakes or faults they may have, scoffing at any high god will not go unnoticed.
Ganesh Chaturthi day is determined by the Hindu lunar calendar and as mentioned earlier, usually falls in the fall, in October.
Annotation:
Sivanadanda, Swami Sri. Hindu Feasts and Festivals. Himalayas, India: The Divine Life Society: World Wide Web Edition: 2000. http://chidananda.org/ download/ hindufest.pdf.