Most of ppl are good at Long positions, and not at all good at Selling short, or close the Long positions. The bias is because most of security market around the world prevent selling short. So when ppl bought it, they hope it goes up, even think a dangerous trend reversal as a normal pull back...
hi horace:
You asked a very good question. I can answer it, because I did quite some intensive studies since later 2009 on trailing stops. I don't think there are anyones who know it better than me.
My findings is: to use the percentage trailing stop can help you greatly improving your trend...