We’re the first to admit it: the notion of brand authenticity is nothing new. Ostensibly, brands have been embracing genuineness and integrity for decades now. The irony, of course, is that the more the concept is bandied about, the less authentic the experience becomes. Call it the inverse law of authenticity.

Of all the ideas related to brands and branding, authenticity should be the one with teeth. It should mean something to say a brand is authentic. The mark of true authenticity, after all, is a visceral connection between a brand and its customers. And the fact is that truly authentic brands outperform their competitors. For this reason alone, a reclamation of authenticity is long overdue.

But just what is authenticity? What does it mean for a brand to be authentic? As is often the case, the easiest way to answer this question is to think of a brand as a person. When a person is seen to be authentic, his personality and actions faithfully comport with his innermost values and principles. So it is with brands. Nearly every brand has some version of a core purpose. An articulated proclamation of why it exists beyond turning a profit, a brand’s core purpose is a fundamental component of its brand compass. Authentic brands look, feel, and act in ways that consistently cohere with their core purpose.

So what’s the most effective way for a brand to embody authenticity? One way is to run constant and continual audits on its various touchpoints, ensuring that each is in accordance with its stated core purpose. As you might imagine, though, this is a pretty tedious and inefficient methodology. A simpler, more powerful way to guarantee brand authenticity is to fundamentally alter the way a company and its stakeholders think about the brand.

As Simon Sinek puts it in his book Start With Why (as well as in a popular TED talk on the topic), “People don’t buy what you do, they buy why you do it.” Sinek comes to this conclusion based not just on anecdotal evidence, but on principals of evolutionary biology. Human decisions are fundamentally driven by the brain’s limbic system—that pre-rational segment informed by emotion and responsible for feelings of trust and loyalty. So when a brand’s actions are motivated by its core purpose (why it does what it does), those actions are aligned with the most primal motivations of its customers.

Where Sinek is concerned, successful companies communicate to customers with messaging that begins with why they do what they do, as opposed to what they have to offer. “Why” is the most viscerally relatable element of a brand’s message—its most powerfully differentiating value proposition. For our purposes, “why” is both the starting point and final criteria for brand authenticity. When every touchpoint of a brand is born from its core purpose (the most fundamental “why”), that is the mark of an authentic brand.

In the long run, brand authenticity saves money by making marketing campaigns seamless and effortless. It maximizes profit by fostering the deepest possible connection between a brand and its customers. The catch is that the authenticity has to be real. You can boast about how authentic your brand is until the proverbial cows come home, but unless your brand experience meets the above criteria, you’re doing more harm than good.

Whether they know it or not, customers will always be able to sniff out inauthenticity. Our brains are hardwired for the task. So why don’t all brands take measures to ensure their experience is authentic?

“Why” indeed.

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A prolific blogger, speaker, and columnist, Brian has more than a decade of experience in design and branding. He’s written for publications including Forbes, Huffington Post, and Brand Quarterly.