Success is only momentary. To maintain the value of your brand you must know and understand the underlying drivers of its success. To understand your brand is to understand that markets constantly change. Today's successes may be tomorrow's failures.
Consider Arthur Andersen's brand. A few years ago, Arthur Andersen was one of the top professional service firms in the world touting itself as "a pioneer in bringing global best practices to the marketplace." Now the firm is a mere shadow of its former self in terms of workforce and reputation. The Arthur Andersen brand value has plummeted.

A brand is a dynamic, ever-changing asset and its dynamics and drivers of value must be attended to constantly to make the most of its potential. 

To create and build your brand, you must identify and understand the underlying change factors, or drivers, of your brand's value.