Hanuman was a monkey, and like all monkeys, he could never be quite still. He swung from branches, jumped over rocks and swam through streams . Every time he saw a Brahmin praying, he found ways to distract him. If the Brahmin was offering water, Hanuman would drink it, if the Brahmin was praying by a fire, Hanuman would douse it, if a Brahmin had a beard long enough, Hanuman would pull it.
Finally the Brahmins had had quite enough, so they got together in a secret hiding place where they lit a fire and prepared a curse: that Hanuman would forget the truth about himself and his powers until he was reminded of them at the time when he needed them most.
Panchamukhi Hanuman pataka, gouache on cotton. Jodhpur. 19th century and Hanuman in the 20th century, taken from a temple wall in Madhya Pradesh.