The Space-Time Continuum of Credit, Debt and Investments

I woke up this morning to hearing a comment, loud in my half-asleep ear, on the radio about how paying off a debt is equivalent to mailing yourself a check from the future to the past. I imagined my past self standing at the mailbox, checking the mail, and receiving a check from my future self, thinking it would be pretty cool if that could actually be possible, and how excited I would feel if I received money from myself, originating from some other time and place. Now I have a thought to amuse myself with every time I make a credit card payment. I wondered if the person who made the comment was trying to say it would be the equivalent of a colossal waste, as the money would be going for nothing, since the past primarily exists only in our minds. If I picture myself in the present, writing out a check to my five-years-ago self, for an airline ticket or a new couch on credit, I am less amused. That past self was so much more carefree and less conscious of my future finances. On the other hand, something purchased in the past with credit or a loan, like a college education, a car or memories of that trip to Spain last year, can often still be appreciated and used in the present and the future. The opposite scenario exists in the form of investments, in which tangible money from the past gives you a return in the future, so it's like your back-in-time self pays you money in the future, which is a bit more obvious and much more easy to understand. I always had trouble trying to grasp science fiction/physics concepts like time travel and space-time continuums. I haven't actually gone to Spain yet, either.