I've never carried a balance on a credit card. In fact, until I was about 16 years old, I didn't know you had the option of not paying off a statement in full. My parents set a very good example by never incurring credit-card debt. I always thought credit-cards were just a convenience so you didn't have to carry cash.

I've continued this good habit of treating credit-card money like your own hard cash to this day. I would only consider extending credit-card debt in an emergency, and hopefully it won't come to that.

Here's where I get fuzzy on the economics of the credit-card system (in part because of my discipline, I've never had to really understand the issues of fees, interest rates, and details of how the money is really made behind the scenes)…

But whenever I get asked “debit or credit?", I always think to myself, “If I have the option, why would I let them take the money immediately, when I can instead keep earning interest until the end of the month?” I understand there are reasons why people choose credit over debit, perhaps the two most common are a lack of discipline regarding credit-cards, or the financial inability to secure a non-debit card.

But beyond that, maybe someone can educate me. Are there any other good reasons to choose debit instead of credit the next time I'm in line at the supermarket or gas-station?