"Sorry, sir. We can't sell you any more shoes right now. Our landlord hasn't come by to pick up our profits from today yet..."
Sound reasonable to you?
It seems like the arrows have nothing to do with the prices of the items. If you buy bananas at at "red" arrow and sell them at a "green" arrow, you lose money! It works better to buy at "green" and sell at "red", but sometimes you still don't make money!