Assuming something is always a good deal because it is on sale
Many people try to “save” money by spending it. From the new outfit on sale at the mall to the great new snack with a coupon at the grocery store, you are not saving money if you buy something you don’t need. If something is on sale and you spend on it when you would otherwise not have bought it, you didn’t get a good deal- you fell into the marketing trap and made a financial mistake. This can seem minor, but when you do it all the time, it becomes a major problem.