system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can the U.S.A. sustain such a large national dept/high percentage of deficit spending? 

Yes, I understand that, unlike countries such as Greece and Spain, the U.S.A. economy is a force the whole world depends on. Even still, why do people place so much trust in the dollar even as such a large percent of our national budget is deficit spending?
gpt
It's pretty simple - people trust that the USA will pay them back.  If people trust you'll pay them back, you can borrow basically anything you want.  In a small way, this is reflected by your own personal borrowing - the higher your credit score, the more people will let you borrow and at lower interest rates.  You can think of it like the US Government has a credit score of infinity.  It is considered pretty much *the* safest place to lend.  You can see evidence of this back when S&P lowered the "rating" of the US debt (lowered its credit score, basically).  People worldwide were scared, but that same day they loaned even MORE money to the US, simply because no matter what S&P said, it was still the safest place to put cash.

Now, yes, this means that the US has to exercise good stewardship of the money, and responsibly pay it back.  Because people will stop trusting it, if it doesn't pay, and then it won't be able to borrow as much.  The reality of the situation is that the US could, if it wanted, inflate its currency and thus reduce the amount it has to pay back.  So it's very unlikely to go entirely bankrupt.  But if it pulls this little trick, people will lose trust and the same effect will happen.

It's not going to last forever.  Countries like China are already pushing for an "international reserve currency" that's not dollars, so they don't have to trust the US.  We'll see what happens.