In the ideal branding world, everything is sunshine, fresh air and puppy dogs. It’s about being faster, smarter, a better value, the family brand, the wholesome brand, the success brand, the coolest, hippest, and cutest, most people-driven product or service you could ever imagine. Brand slogans exude upbeat, self-affirming energy: I’m Lovin’ It; The Pursuit of Perfection; Baseball, Hot Dogs, Apple Pie, and Chevrolet.

The positive side of branding is the side that marketers control and in a perfect world, it might be enough. But, of course, in the real time journey of building a brand, the sun goes down, puppies grow up, and stuff, as they say, happens. Brand managers like to focus on offense, but there comes a time when most brands have to play a little defense as well.

The irony of having to defend a brand and preserve its equity is that so often the damage is self-inflicted and often preventable. The key element to gauge is the level of outrage by the customer and ultimately by the public. A disappointed customer who found a foreign object in his cereal is one thing. An enraged public is quite another.

Let’s start with the former. You make a million widgets every month, there’s going to be a few glitches. Hopefully your quality control processes pick up most of those, but when problems become obvious to your customers, look out. VW is a case in point. It’s a venerable brand with a long history in the U.S., but in 2002 they began to see their sales drop in this country. By 2005, they had lost over 30% of their unit sales. VW offered various reasons to the trades and their dealerships, but it wasn’t that hard to figure out. Just ask a few people who were driving VWs at the time how they liked their car, and you often heard stories of numerous defects, trips back to the dealer, and arguments over warranty coverage. Surveys by J.D. Power and Consumer Reports showed that VW was at or near the bottom of quality and reliability ratings. Positive brand slogans about “Drivers Wanted” and “Das Auto” began to ring hollow in the ears of customers who swore they would never buy another VW. The German carmaker was slow to acknowledge their quality issues and now, even with a better track record on quality, their sales in 2009 were the lowest in the U.S. since 1998.

But VW can thank their lucky lederhosen that their quality problems and slow response stayed largely between them and their customers. Brand building is tough enough without having to answer to the media and being run over by each day’s news cycle.

Just ask Tony Hayward.

Mr. Hayward is the now former CEO of BP who was thrown into the tsunami of global reaction to the Gulf oil rig disaster and managed to make it even worse for BP with his inappropriate comments and surprising ignorance of the details of the situation. Unlike VW, BP’s quality control problems, which likely led to the disaster, were perhaps less rampant, but far more devastating. After a few weeks of media and congressional hammering, Hayward’s comment of “I want my life back,” was about as insensitive a remark imaginable considering the 11 fatalities from the explosion and thousands of other lives that had been dramatically altered by the disaster.

The BP event was one of the year’s biggest stories; it put a searing spotlight on a brand that claimed to be green and “Beyond Petroleum,” yet the real irony may be they will be less damaged in this country than VW was for making a million shoddy cars. Sales at BP gas stations were affected at some locations, though not all of them, and many station owners are reporting a slow return to pre-disaster levels. To their credit, BP has diligently spread positive PR and advertising about their efforts to make things right and appear to be offering the financial resources necessary to help those affected by the disaster. I doubt, however, that we’ll be hearing much about “Beyond Petroleum” for some time. Nor will there be any new franchisees eager to open a BP station, when they could chose from many other brands.

And that’s one of the true downsides of the dark side of brands and brand experience. The pain lingers. A bad experience with a brand, especially when it involves a large expenditure, can create antipathy that lasts years, even decades. Mega-brands like VW and BP correct their problems and move on, but their brand perceptions can be toxic to growth even years later. Smaller brands may not be so fortunate. So it’s easy to say avoid the negatives and you’ll live happily ever after, but the point is that a seemingly harmless way to cut costs or speed production may still weigh heavier than all the positive messages a brand can muster.