This is like saying that all that matters to your bank account balance is dollars in and dollars out. It's obviously true in the most trivial sense, but it's not useful advice. There are countless other factors that affect the amount in and amount out.

If someone is trying to increase their bank balance which advice is more likely to help them: "Just increase your dollars in or decrease your dollars out" or "Get a roommate, move to a less expensive neighborhood, cook your own food instead of eating out"?