Historically, Piccolo is almost always the character who recieves the most beat-down first off. He was killed in the Saiyan Saga, brutally man-handled in the Cell saga (how was he not killed? Regeneration or not, that should have killed him), Brolli put some holes in him, as did what's-his-name in World's Strongest... He just can't stand on his feet for too long without being knocked off of them. In the late-Cell-saga when he was attacked by Cell Jr.s he was probably the only character who was prepared. Goku was tired, no doubt. Vegeta was a little humiliated by Goku's performance and he wasn't expecting to fight at all. Trunks doesn't know how to fight... well you get the picture. Piccolo is the man. He has probably recieved more training than anyone on the show thanks to his Multi-form technique, and keep in mind he also absorbed Nail's training on Namek. The man knows how to fight, and that goes a long way. Ask Tien.