Marketing is about movement; taking a brand from here to there. And all movement follows three simple laws of motion first articulated by Sir Isaac Newton in 1687! Here they are (there are only three, so even you should be able to understand and remember them):
1. AN OBJECT AT REST TENDS TO STAY AT REST UNLESS AN UNEQUAL FORCE IS APPLIED. AN OBJECT IN MOTION TENDS TO STAY IN MOTION UNLESS AN UNEQUAL FORCE IS APPLIED. This basically means that success (forward motion) tends to breed more success. Ditto for Failure (rearward motion). If you're on a roll you have demonstrated this. And if your share is plunging you're demonstrating the law too.
2. THE UNEQUAL FORCE (above) REQUIRED TO CHANGE THE DIRECTION IS EQUAL TO THE MASS OF THE THING TO BE MOVED AND THE SPEED AT WHICH IT IS MOVING. This if F=ma (force equals mass times acceleration). Large, slow moving companies are easier to knock off their position by smaller, fast and more agile companies. That's how General Motors got displaced by Toyota et al, how iTunes completely reconfigured the retail music market and Amazon is changing virtually every retail category.
3. WHEN YOU EXERT REAL FORCE, THE BODY (company, brand) ON WHICH YOU EXERT THAT FORCE WILL MOVE
There are lots and lots of clear demonstrations of the profound truths of these laws. In 1998, as part of the first online shopping promotion on behalf of American Express, we gave participation to retails on the condition that they made the American Express card their default choice. More than 15 years later many still have not changed that; the object in motion stayed in motion.
I mentioned GM as a victim of the second law and iTunes and Amazon as perpetrators. Quick...name 10 more examples. Hint: most of the largest, most successful companies you can think of didn't even exist 20 years ago. They displaced others by taking advantage of new technologies, moving faster and being more decisive than their dinosaurian predecessors. Think Google replacing the Encyclopedia (but with Wikipedia finding a brilliant niche to occupy). Think eBay and Craig's List decimating the classified ads in newspapers.
This is worth thinking about because inertia is the #1 enemy of success. It lowers the amount of energy (or money) necessary to displace once powerful brands. Where does your brand live on this continuum?