It's what adds a lot to the genre. Thing is although you can see someone while the other player can't, you can't shoot him until you are in a view to be seen. It happened to me many times where I was flanked by someone ready to kill me and I was able to turn it around. Take for exemple counter strike. It takes a lot of practice to be fast and skilled but one thing I can tell is you need to be ready to encounter someone after every single corner. In the end it's fair for everyone because we all can use it at our own advantage.