Here's the reason helicopter money (quantitative easing, aka QE) works: if the USA inflates its currency by creating a bunch of new money and giving it to its businesses or citizens, people outside the USA who are holding US dollars will find that their dollar isn't worth as much. QE transfers value from outside the country to inside the country.

But the dirty secret is, everyone is thinking about employing QE to stave off their country's upcoming recession. And if everyone pulls this little trick at once, it won't work for anyone at all!