Well, I heard from people saying that I should change the string regularly, because if not, it would lose the gripe/bite and whatever ball you are hitting is just going straight to the net. I can tell at impact whether a ball is well-hit...or just straight to the net, but yet the stroke is the same. So is it the string or my own technique. I've been playing with my current string for 5 weeks, gosen polylon. Not exactly a grippy string to begin with.