We have a similar phrase in our house, that goes something like this: "what will you do with that, thirty minutes after you've bought it?" If it's going to sit on a shelf unseen, or go into a box, we usually don't buy it as a matter of principle. Sometimes to practice self-discipline, we'll ask each other "did you want that before you saw it in the store?" If the answer is "no", we challenge ourselves to hold off on the purchase until a later date. We find that oftentimes the "wanting" goes away as soon as we leave the store. We might even say "no" to something we could otherwise afford, just to prove that we're the masters of our wallets, and not the other way around.
That's a great idea!