The basis for working with, and modifying, habits comes down to the creation and reinforcement of neural pathways.
Our brains are made of neurons. If you imagine the habit of putting on your seat belt, there is a sequence of events that occur. You sit, your arm reaches across to grab the belt, your arm pulls it across your body, and then inserts the buckle. For the sake of this example, imagine there is an individual neuron responsible for each step. All the neurons connected together to form this action, this behavior, is a neural pathway.
Once these pathways are established, and are 'triggered', they function automatically. Depending on how they were created, and what reinforcement they have had, they can be very difficult to change.
Behaviors, Habits and Beliefs
If you consider a simple habit, like locking the door or putting your seatbelt on once you get in your car, it is an automatic function. You do not consciously think about doing it. It is a dominant neural pathway generally created via repetition. Most people can change this habit given time and reason. People that have had a traumatic event around one of these functions, such as being followed to their car or experiencing an auto accident, may have a much more difficult time changing this habit. Their neural pathway was created by repetition and reinforced by strong emotion. If they were to try changing this behavior, they would be working 'against' a dominant neural pathway with a strong emotional association.