Why do you consider this income? Because it's shown on a piece of paper? But we know that the Internal Revenue Code of 1986 enacts a tax on income, not on pieces of paper.
Let's say I'm walking down the street and see IronMan, who owes me $100 for a used anvil I sold him last week. He pulls out his wallet and starts to hand me a Benjamin. But a thief runs by and yanks it out of our hands just as the transaction is about to be completed. Do I have income? Do I have a deduction? Does he still owe me some money?