As much as we all promise ourselves that we'll only buy things we absolutely cannot live without, sometimes in the heat of the shopping moment that mentality is substituted by one of like not love. I know there are some items in my wardrobe that fall in the camp of wish-I-never-bought-it, and perhaps that remorse could have been prevented by using this logic.
Salaries are tricky in getting us to think about our income in yearly or by-paycheck terms, but it may pay off to break down your salary (after taxes) in terms of hourly compensation. When you're holding up a cool sweater that you don't necessarily need, look at the price tag and compare it to the number of hours you worked to earn that sum. So, if you're eying a $150 sweater and earn the equivalent of $30 an hour, ask yourself if it's worth five hours of work.