Because a default -- even a "technical" default in the form of an extension or renegotiation -- indicates a serious problem in a country's finances, which can a

Because a default -- even a "technical" default in the form of an extension or renegotiation -- indicates a serious problem in a country's finances, which can affect its credit rating and, in turn, its ability to continue borrowing as well as the value of its currency. The U.S. has defaulted before, in 1933, but this would still be considered a very significant event in global economics, and economists really don't need another reason to get nervous right now. There is, by the way, an interesting elephant in the room that I've yet to hear mentioned anywhere: once we've gotten to the point that people start discussing the possibility of simultaneous defaults of several major countries, nobody's really sure what will happen next, and, nobody's really sure how to get out of the hole, since we've never been in this deep before.