Painful Memory

In 2005, I was playing an underrated elementary age youth late at night at the Spokane Chess Club. It was part of one of our summer quad events. A critical position was reached when he played 21.bxc3 and offered a draw. I was down an exchange plus a pawn.

Black to move

The next morning I awoke from a deep sleep at about 3:00 am and immediatly set up the game in Fritz. I required less than five minutes to demonstrate what I should have seen several hours earlier.

What did I learn in my sleep?