When the Pandavas were little boys, their father Pandu and their mothers Kunti and Madri lived in exile in the forest. Pandu brought his sons up in that secluded austere atmosphere, with only sages and ascetics for company, and every day Pandu would sit his sons on his knee and teach them how to be honourable men.
One day when Pandu sat Sahadev on his knee, he told his littlest boy
You must consume my brain. Only then will you be able to know all about this world.
Then Pandu died.As Pandu lay on his pyre, the Pandava brothers stood with Kunti and watched. The fire was slowly eating it's way through the corpse and as Pandu's head burst from the heat, Sahadev saw his father's brain.To his child's mind he knew exactly what he had to do. It was his father's order. Without a word Sahadev ran up to the flames and reached in, plucking out the matter. While his elders yelled and shrieked, Sahadev took off into the forest.
Krishna, meanwhile, was far away in Mathura but he knew what was happening. He also knew that if Sahadev managed to do what he wanted, it would be a disaster. Taking the form of an old sage, Krishna manifested himself near where Pandu's body burned and chased after Sahadev.
But the little boy had already taken a bite of his father's brain. And with that bite he became enlightened about all that had happened in the history of the world. With a second bite, he became enlightened about all that was happening in the world. And with a third bite, he became enlightened about all that would happen in the future of the world. Sahadev became 'trikal gyani' - a knower of the three times - and even though he was only a little boy he realised that the old sage who was chasing him wasn't really an old sage but the Supreme Lord Himself.
Sahadev stopped.Krishna caught up with him, heaving an exasperated sigh for it was too late. Sahadev knew everything.