Let's put this in terms we can all understand

So I was talking to my friend Joe Tackspaier the other day and he told me about some of the financial problems he's having. Apparently he let's his girlfriend use his credit card and she recently went on a shopping spree at the mall and bought $7,800 worth of clothes, shoes, and other stuff. When she told him about it he was a little upset but she calmed him down by explaining that she got a bunch of stuff on sale and that normally it would have been $9,000 so really she saved him $1,200 and besides, it's stuff they "need" anyway. The problem is that Joe only makes $27,000 a year plus they're already $107,300 in debt. To me it's pretty obvious that they are never going to be able to climb out the financial hole they've dug for themselves.
Part of the problem is that Joe doesn't really understand how money works and thinks that because she's putting this on a credit card it's not that bad - that someday in the future he'll be able to pay it off much more easily.