This is especially true of money you receive from other nations that is supposedly backed in the same way. Distance makes people bolder and less hesitant to break promises. People can probably be trusted when times are easy and when prosperity reigns, but when times are tough, promises are much easier to break than the laws of survival. This is what makes self-reliance of an economy important. This is why local industry and agriculture should be protected.
Productively ability is the real source of wealth of the nation.
However, natural disasters also occur. While the world as a whole may be fairly stable, the area around you is much more prone to random fluctuations of climate and geology. Thus self-reliance is not the entirety of a secure economy, but merely the supporting structure. The secondary source of security is prosperity in other geographical locations. The more prosperous others are, the more likely they will come to your aid in times of trouble.