Uddalaka could tell from Shvetaketu’s boasting about how much he’d learned that he hadn’t learned anything at all. Or at least nothing really worth knowing.
“Did your teacher teach you how to hear that which can’t be heard or know what can’t be known?” Uddalaka asked. “Oh-oh. That wasn’t in the curriculum.” “Go outside and get me a fruit from the banyan tree.”
Shvetaketu ran outside for the fruit. “Now cut it in half,” his father instructed. “What do you see?” “I see the seeds, Dad.”
“Cut one of those in half.” This wasn’t very easy, banyan seeds are extremely small. Finally Shvetaketu managed to slice one evenly. “What do you see?” Uddalaka asked.
The boy was baffled. “What do you mean dad? There is nothing there.”
Uddalaka looked his son in the eye, “From that ‘nothing’ an enormous tree arises. When you understand what ‘nothing’ is, you will understand yourself. The nothing you can’t see is the very essence of the reality of the tree. The unperceivable essence of being is also what you are. You are that, Shvetaketu.”
“Pour some salt into this bucket of water,” Uddalaka continued. Shvetaketu obeyed. “Now give me the salt back.” “I cant do that!” Shvetaketu objected. “It is gone!”
“Take a sip of the water. You taste the salt, don’t you? You couldn’t see it, yet it was there all along. Just as the salt pervades the water, so the subtle essence of reality pervades your body. That subtle essence is true being. You are that, Shvetaketu.”
Source [Slightly adapted]