If you are a life-long GM buyer, its going to be really easy to sell you another GM, and really hard to sell you a Ford.
Its not just habit. Confirmation Bias selectively chooses the information that confirms what we already believe to be true, and ignores information to the contrary.
That doesn't mean you can't sell a Ford to the GM buyer, but its going to require an inordinate amount of resources to make the sale compared to a current Ford buyer.
Keeping your current fans happy should be your first priority.