Nike and Reebok started in roughly the same place. Both athletic shoe companies, both competing in the same core market, both looking for the next source of growth once their initial category matured.
One of them found a repeatable formula for expanding and used it again and again. The other kept chasing a different growth story every year, with uneven results.1
Zook and Allen's case study of the two companies makes the contrast explicit:
"Both companies had started out in the same business... Yet Nike found a formula for growth that it used successfully again and again, while Reebok seemed to pursue a different source of growth every year with uneven results."1
The difference wasn't effort or ambition. Both companies wanted to grow. The difference was in how each company expanded — whether new markets built directly on an established strength, or whether each new venture was closer to starting from scratch in an unrelated direction.
Swift's pop crossover, in this reading, was structured more like Nike's pattern than Reebok's.
The expansion into pop wasn't a pivot away from what already worked — confessional songwriting, teenage relatability, a specific narrative voice. It was the same core strength, extended into an adjacent market that could recognize and reward it, rather than an attempt to become a different kind of artist entirely.
That's the structural definition of adjacent-market expansion: the new market is genuinely new, but the thing you're bringing into it is the same thing that already worked, not a wholesale reinvention built from nothing.
The word "adjacent" is easy to nod along with and hard to actually apply, because almost any market can be described as adjacent to almost any other market if you squint enough.
Country and pop music aren't the same audience, but they overlap more than, say, country music and enterprise software would. That overlap — shared distribution channels, shared media coverage, listeners who cross between the two genres regularly — is what made this specific expansion "adjacent" rather than a leap into something genuinely foreign.
Reebok's problem, on this reading, wasn't lack of effort. It was that each new venture the company chased didn't actually share that kind of structural overlap with what came before it. Athletic shoes to fitness culture to fashion to celebrity endorsement deals, each pursued as though it were the natural next step, without the same underlying audience and channel overlap that made Nike's specific expansions compound on each other instead of starting over each time.
You're looking at your next growth opportunity, and there are two very different ways to reach for it.
One approach treats growth as license to try something completely new — a different market, built around different strengths, hoping ambition and effort carry you through the unfamiliar territory. The other approach asks a narrower question first: what's the closest adjacent market where the thing I'm already good at would still be recognized as valuable, just by a slightly different audience?
The second question, answered honestly, usually points toward a much more repeatable growth formula than the first.
The Nike/Reebok comparison comes from independently-documented business history, not from this book's own research — it's a well-established case study Zook and Allen use elsewhere, applied here as an analogy. The tension: analogies between industries this different (athletic footwear, music) can illustrate a structural principle without proving it transfers cleanly — the specific mechanisms that made Nike's formula repeatable in footwear aren't necessarily identical to what made the pop crossover work in music.
The book uses this comparison mostly to validate a decision that had already succeeded, rather than to genuinely test whether the Nike/Reebok distinction predicts anything in advance. It's a useful frame for understanding what happened after the fact; it's less clear the same frame would have reliably predicted success before the crossover occurred.
Zook & Allen Differentiation Strategy — this page and that one are drawn from the same underlying research program. Differentiation explains what to protect; adjacent-market expansion explains where to grow without losing it. Together they describe a complete strategy: hold your core steady, and expand only into territory close enough that the core strength still travels with you.
Premature Core Abandonment Trap — adjacent-market expansion done correctly is precisely what avoids this trap. The pop crossover extended the core strength into a new market; it didn't abandon the core strength in pursuit of the new market, which is the distinction that separates Nike's pattern from Reebok's.
Sharpest implication: the question worth asking before any big growth move isn't "is this a good opportunity" — it's "does this opportunity let me bring the thing I'm already good at with me, or does it require me to become good at something else entirely first."
Generative questions: