I honestly believe whether you pass or not, given that you have decent driving ability, is largely based on luck. I have failed 3 times, sent an appeal for the last failure and waiting for a response. I drive with a provisional license with my dad in the passenger seat and often, although illegally, have my friends in the back when giving lifts. All of them have told me i am marginally better than other people who have passed their test and that they feel much more comfortable with me behind the wheel compared to those who passed which says a lot really.
Most of the people who pass on their apparent first or 2nd try i know are generally stupid people who failed their theory test multiple times. This one guy i know failed his theory 5 times, passed first time on the practical and lost his license not even a month later for receiving too many points too soon. I'm afraid driving tests are one of those things in life that you have to wait to get lucky and as a result of that, some pass before others even when it's undeserved and you just have to move on.
Classic example of "life isn't fair".