Originally Posted by Myst

John is convinced he lost $20. That is the amount of money he took out of his pocket, that is all that belonged to him that he lost.

Johns wife is convinced he lost $30. He lost the $20 in buying the TV (John had believed the TV was worth $20 at the time) and $10 later (John attributed a value of $10 to the TV later that he lost)

Johns brother thinks he lost $40. $20 originally, $10 in the worth of the TV, $10 that was not paid to him.