I live outside the US, and diversify my investment by buying Exchange-traded notes, which are a combination of the X most succesfull stocks in my local stock exchange. Should I also diversify my investment abroad, or it is safe enough to assume my local stock exchange will, on average, be successfully over the years?
There is a cost (money + attention) to diversifying abroad, so the answer can't be an automatic "yes", but rather some conditions (including sum of investment, ...?)