Let me ask you a question: what is the first thing you do when you get in your car?
No, "turn the car on" is not the right answer. You need to start getting in the habit of locking your doors as soon as you are in the car. It took me a bit of time to practice, but now I have it down so that I am locking the doors as I am closing mine. And I only unlock my door if I am by myself. Why should we worry about this? Because this is the time when a car-jacker will take advantage of us if they are looking for someone to take advantage of.
Sitting in the car, turning it on, setting the radio, talking to someone with you, not really paying attention to anything outside your bubble, you may be surprised when your door opens and someone not so politely asks you to exit your car.
You think this doesn't happen? Or you think it wont happen to you? It does, and it could, so minimize the risk and lock that door before you do anything else. Now you can enjoy that bubble better.