There is a limit to how much money an individual or country can borrow. We all intuitively know this. If you grow your debt faster than your income and your ability to service the debt over a long period of time, people will eventually stop loaning you money. This is true for individuals, businesses, and nations. The end result is a restructuring of the debt (default by one of several means, including serious inflation) or a very reduced standard of living (by previous standards) for a period of time in order to service the debt. For individuals, that may mean cutting off the cable, no eating out, no vacations, etc. For countries it means reduced government programs and benefits, and higher taxes.
The Endgame Headwinds | The Big Picture
This is worth reading in its entirety.