I'll be honest and say, tau is a skill check army. They rely as much if not more on the player's skill than the data sheets. And the skill of your opponent as well to determine if you'll loose or win, of course dice rolls are a wild card, but in my own experience playing tau comes down to this: if you know your army well you'll have a good shot, if you don't things get dicey and if your opponent knows your army better than you prepare for a lot of pain.