I have been an admirer of Warren Buffett since I first read about him in the 1970's in a book SUPERMONEY by Adam Smith the very good sequel to the brilliant THE MONEY GAME. (Both books are highly recommended)
Mr. Buffett is famous now and is widely quoted as he deserves to be. But my favorite comes from an answer to a question asked at one of the annual meetings for Berkshire Hathaway a decade or so ago. The shareholder asked Mr. Buffett's opinion on the outlook for Japan. Mr. Buffett responded by saying it was a good question, but he did not feel particularly qualified to answer. Then he continued (from my memory, not word for word) when I think about something I decide if it is important or not and is it knowable or not. If it isn't important or if it isn't knowable I don't spend time on it. Your Japan question is important, but for me it is not knowable so I don't think about it.
That remark stopped me cold as I realized how smart that is and how completely I failed in that regard. I still fail at it but I am improving.
Is it important, is it knowable? If it isn't both don't spend time on it.