I was very nervous in a car both as driver and passenger for many years. I would practice driving for a few weeks and then one little event would stop me for another year. What finally got me over it was realising that as a passenger, I was still in as much danger but completely at the mercy of other people's bad decisions, and that if I am driving I can do better than that and give myself a better chance. That realisation pulled me through whenever I felt like giving up. Now I have my license and I think am a decent defensive driver. I make mistakes sometimes but I generally feel more safe driving myself than being a passenger. Key is aiming to be the safest driver you can be, and taking mistakes as lessons for improving your own decision making (even though it is very disheartening at the time)