In the battle between paper and plastic, paper is the undisputed winner. Consumer psychologists have found that people are less likely to splurge when they only use cash. And this makes perfect sense. It's always easier to limit yourself to a predetermined amount when using dollar bills. Once you run out of them, you have no choice but to run to the ATM for more. In the case of credit cards, we can have a credit limit of, say, $8,000, a fact not lost on us when we're at the mall. Thus, we feel less predisposed to put the brakes on our purchases when we know we can just swipe the card countless times. Using cash also "stings" more because you actually feel like you're losing something. You can open your wallet or purse and see that your hard-earned cash is no longer there. With credit cards, you can postpone feeling the sting until you receive your bill in the mail, which is what the vast majority of consumers would rather do. Let's not forget that ca...