To what extent should you be focused on external events as it relates to your finances?

You have probably heard a large amount about the Greek debt crisis, particularly in recent weeks and months as it comes to a critical point in determining whether the bailout will be extended by Greece's lenders (primarily the International Monetary Fund and European Central Bank) and on what terms.  To the extent the two sides fail to reach a deal by the time the current bailout expires on June 30, Greece may be forced to exit the European Union.  Considering how far apart the sides are and the fact that the Greek PM has called a national referendum on the proposed terms of the extension of the bailout program, right now it looks likely Greece will end up defaulting on its debts and perhaps leaving the European Union.  

No one has any idea what effect a failure to reach a compromise and/or a subsequent default and exit from the European Union would have on markets.  Some are saying that it would be a relatively contained event that would have little effect on either the European Union or global financial markets.  Others, and I count myself in this camp, think that there is no way to know what kind of effects it will have.

The problem with being able to judge the effects of external events like the Greek crisis or the failure of Lehman Brothers in 2008 are several. First, no one has any clue what effect these events will have on markets.  Seven years later we are still dealing with the aftermath of the financial crisis that, in my opinion, really began to get really bad when Lehman Brothers failed.  No one at the time would have been able to tell you how long it would take us to recover from the financial crisis, to the extent you believe we have even recovered at present.  Secondly, the ability to tell when to pull out of and then get back into a certain asset class or the stock market is also extremely difficult.  I am skeptical that even the people on Wall Street are any good at it.  

Personally, I try not to be too worried about external events because I have seen studies that say people who pull out of the market invariably do much, much worse over the long term than those who leave their money in even when the market it is dropping like a stone.  To me this applies to both stocks and bonds. As nerve-wracking as it may sometimes be, I think you are always better off staying the course.