It used to be said that if America's economy caught a cold, the rest of the world would catch the flu. I'm not so sure that is the case given how interrelated the global economy has become in recent years, but it's tough to look at these numbers and not gasp. Note that it wasn't just London's FTSE that got hammered today. The German DAX and French CAC 40 dropped about 7% each. HOLY SH!T! I would guess there's going to be some angina on Wall Street tomorrow.
If you have money in the market for the long haul, then this sort of thing is likely to be just a bad memory some time from now. I've seen enough downturns to know that the market is cyclical and our economy is resilient. And I'm confident in the economic underpinnings of America. On the whole, we're smarter, harder working and more innovative than any other country on this planet. This too, we will survive.