A front page article in last week’s Wall Street Journal documented the demise of Liz Claiborne, one of women’s fashions most successful product lines for 34 years. The company that pioneered working women’s apparel after its introduction in 1976, Liz Claiborne has been removed from virtually every tony retailer and is now available exclusively through JC Penney.

It was a precipitous and entirely avoidable fall.

Liz Claiborne broke the first commandment of branding: Be true to your clients and yourselves.

Claiborne made its name by designing stylish career wear for the millions of women, particularly younger women, entering the workforce. Their pieces were consistently styled and well made, delivering a specific brand promise to the women who stocked their closets with Claiborne ensembles that could be mixed and matched to create multiple outfits from a handful of separates.

Claiborne developed a loyal and trusting following of women who appreciated her collections. But with her retirement from the company in 1989, the brand began to suffer. There was no designer who shared Liz Claiborne’s design aesthetic and without a design leader, the company regressed to a financial leader whose focus was the bottom line, not the hemline.

Design by committee emerged, diluting the Claiborne brand promise in a fruitless pursuit of the youth culture. Their working women loyalists took notice and turned their backs on uninspired and confusing Claiborne collections that were considered fashion forward but not geared toward working women, the brand’s core constituency.

The dispiriting Claiborne story was in sharp contrast to the story that Jay Greene recounts in his book Design is How it Works. Porsche has remained remarkably successful in an industry that has few perpetually thriving automakers. Porsche attributes their success to an unyielding devotion to the design principles encompassed in the very first 911 that debuted in 1963.

Since their very first car, Porsche has remained true to its design DNA by incorporating specific design cues – intakes instead of a radiator grill, a car that always tapers to the rear, open wheel rims to display the strong brake calipers, front fenders always higher than the hood, ignition always on the left of the steering wheel and vertically oriented dashboards – that support their vision of a car that is all about driving performance and authenticity.

Porsche has never varied from a design approach that produces cars that their own designers crave. They never cut corners. They never adopt trends that risk the company’s credibility. And they never try to appeal to everybody.

Porsche designers intuitively understand the desires of their most passionate drivers and develop new cars with them in mind. Liz Claiborne took a different tack and abandoned their brand promise and with it their most loyal clients in pursuit of a younger, more active customer. They alienated their most loyal customers without generating any traction with the fickle and trend conscious youth market who want nothing to do with the company who makes clothes for their mothers.

Porsche has had an endless string of hits, including their Boxster, Cayman, Cayenne and Panamera and reported record profits in 2009. Liz Claiborne has virtually ceased to exist. Breaking your brand promise appears to have severe repercussions. If only the Claiborne executives drove Porsches, they’d understand.

How many other successful brands have hastened their corporate demise by abandoning their core principles and their most loyal customers? Sadly, I’ll bet it’s long. Real long.