Rant: Balls

I've never understood why tennis players always get a second chance at serving. It seems like at least half of the balls from their first serves hit the net or don't land in the appropriate area on the other side of the court. Are these players crap? Why should mistakes be allowed? You don't see many double faults because they always seem to manage to serve correctly the second time. So they can do it. How about penalising them if they mess it up the first time? I don't pretend to be any good at tennis myself but I don't see the enjoyment of watching it when they have daft rules like this that, to my mind, don't bring out the best in the players and don't contribute positively to the spectator aspect of the sport.