Originally Posted by Ifihadaboat

To back up Global's point with math that even I can understand:

If you start with $10 and return 100% (10+(10*1)=20)the first year and -50% (20*.5)the second year you are left with the exact same $10. But your average return (100+-50 divided by 2) is 25%.

This is the reason that you cannot use the average (mean) of investment returns.