Spending on Credit means spending future money, if any

Today, I was topping up some clothes at FOX when I witness a disenchanted state of affairs. Two ladies in their mid twenties were in front of me in the queue. They saw the promotion for a certain bank's credit card at the counter and began to discuss on whether they have that particular bank's card. One of them whipped out a stack (that must have been 2 cm thick) of credit cardS. She lamented, 'I think I have that card, but I do not know whether I can use it because I have not paid off the bill'. Wow.