You're at the Wallyworld. You go to the self-check line. Bleep bleep bleep, you're through scanning your stuff. Time to pay with the trusty debit card. Declined. You know for a freeking fact you have enough money in there. Okay, so you try it on "credit". Declined again.
You do not KNOW anything else, except that your card seems to not be working. Then you look around and discover that several other checkers are looking at their registers with funny looks and scanning and re-scanning credit and debit cards. Apparently it's not just you, it appears it's everyone.
So, what do you do now? Use your cash and buy whatever it was you just ran through? Cull your stuff before purchasing? What's going through your mind right about now?