Could you explain me in English what "the demands of interest" in the following text means? The text is from Steven R. Covey's book The 7 Habits of Highly Effective People: Powerful Lessons in Personal Change - see excerpt here.
"I want it now." People want things and want them now. “I want money. I want a nice big house, a nice car, the biggest and best entertainment center. I want it all and I deserve it.” Though today’s “credit card” society makes it easy to “get now and pay later,” economic realities eventually set in, and we are reminded, sometimes painfully, that our purchases cannot outstrip our ongoing ability to produce. Pretending otherwise is unsustainable. The demands of interest [emphasis added] are unrelenting and unforgiving. Even working hard is not enough. With the dizzying rate of change in technology and increasing competition driven by the globalization of markets and technology, we must not only be educated, we must constantly re-educate and reinvent ourselves. We must develop our minds and continually sharpen and invest in the development of our competencies to avoid becoming obsolete.