Coke vs. Pepsi: Example of Brand Loyalty and Preference

How do you define brand loyalty? It is the state in the customer's mind where he is willing to go the extra mile just to get the brand he wants. I think it was a Heinz ketchup executive who gave this example: if the customer went to a supermarket looking for Heinz and did not find it among the ketchup displayed, will then postpone the purchase or go to another supermarket just to buy Heinz. For a child, that explanation would be too long. For the child in this vendo commercial, the extra mile is 2 cans of Coke. (not sure though if this is a legitimate commercial that actually aired.) Wouldn't you like to be the preferred brand?