Yesterday somebody asked what is onam festival, and why it should have so much of pomp I told him this is the mythological story of Vamanan, one of the dasavatharams of Sri Mahavishnu. Vamanan came to punish Mahabali the Asura king who was boastful of his dharmic nature. Vamanan asked for three steps of earth, which Bali said he will give. He was warned against this by many but Bali gave the land in principle. Vamanan measured the earth by one foot, the sky by the second foot and asked where he will place his third foot. Bali showed his head, on which Vamanan placed his foot and suppressed him to eternal glory.
This is the occasion of the triumph of good over the evil, some say. Some others say it is the post harvest festival of prosperity. Whatever it may be people enjoy after the onset of rains.