A product differentiator is defensible when copying it would cost a competitor more than they are willing to pay. That cost can be money, time, an existing business they would have to damage, or a change to how their own company is run. A feature charges nobody anything. A competent rival reads it, understands it and builds it inside a product cycle, and from then on it is part of the category. When a company asks me whether the differentiator it has just built will still be theirs next year, these are the three things I look at.
Defensibility is counted in years
Investors already price this question, and they price it as a duration. Morningstar rates a company wide moat, narrow moat or none, and the rating is a judgement about time. Its published methodology puts a narrow moat at excess returns "more likely than not" for at least the next 10 years, and a wide moat at excess returns very likely for 10 years and more likely than not to remain for at least 20. A company with no moat sees its returns fall back towards its cost of capital sooner than that. Morningstar names five places a moat comes from: intangible assets, switching costs, network effect, cost advantage and efficient scale. A product feature appears nowhere on that list. That absence is the useful part of the rating for a product team. Ask of your own differentiator what an equity analyst asks of a company: how many years before somebody else has it.
The odds are harsher than most teams assume. A McKinsey study of 2,393 large companies, published as Strategy Beyond the Hockey Stick (Wiley, 2018), plotted their economic profit over a decade and found that a company sitting in the middle three quintiles had roughly an 8% chance of reaching the top quintile ten years later. Position turns out to be sticky in both directions. That is the argument for treating a differentiator you already hold as an asset that has to be defended.
A durable differentiator has a barrier behind it
Hamilton Helmer's 7 Powers: The Foundations of Business Strategy (2016) gives the clearest account I know of where durability comes from. Helmer defines Power as "the set of conditions creating the potential for persistent differential returns", and names seven: scale economies, network economies, counter-positioning, switching costs, branding, cornered resource, and process power.
The part product teams skip is the structure underneath the list. Helmer holds that each of the seven has two components, a benefit and a barrier. The benefit is the improvement a customer feels and the business can see. The barrier is what stops a competitor reproducing it. Benefits are common. Barriers are rare. A feature is a benefit with no barrier behind it, and that is the whole reason it is copied.
Place your own differentiator against the seven and be strict about which one it sits in. Most claimed differentiators turn out to be a benefit still looking for a barrier. The ones that do land tend to land on branding or counter-positioning, because those two are the hardest for a well-funded competitor to simply buy.
I led the go-to-market design for Philips OneBlade. It launched under the line "this is not a shaver" and reached €55 million in its first year. The product itself was copyable, as products are. The position was the harder thing to reach, because a competitor built on the razor category could not put that sentence on a box without arguing against its own shelf.
The copying that matters happens inside your own company
In the previous piece I ran the copy test from Jay Barney's VRIO and said the organisation question is where most claimed advantages fail. It is also the part of defensibility a company controls directly.
A barrier is the accumulated effect of decisions that keep going the same way. Those decisions are roadmap trade-offs, hiring briefs, pricing exceptions, a supplier chosen on unit cost, an integration accepted because a large customer asked. None of them announce themselves as strategy. At three people, the differentiator survives on shared memory. At fifty, shared memory has gone and usually nothing has replaced it, so the decisions start averaging back towards the category. Nobody copied you. You spent it.
Flowdonia's method, Differentia, calls this the Bond: translating the differentiator into principles for every layer and touchpoint, co-created with the teams who own them, so it becomes how they work. It has landed when a junior in any team can name the differentiator and explain why their decision served it.
A test to run this week
Write down your differentiator, then write the barrier under it in one sentence, without the word "better". If the sentence only describes something good for the customer, and names nothing a competitor would have to overcome, you have your answer already.
Then put a number of years on it. Brief the person who would lead the copy if they worked for your closest rival, and ask them for three figures: how long, how many people, how much. If nobody in the room can name a year, what you are holding is a lead. A lead is spent.
Last, pull the ten most recent decisions your teams made without you in the room. For each one, say whether it strengthened the barrier or drew it down. The pattern in those ten tells you how long the differentiator has left, and the number is usually smaller than the one the competitor question gives you.
Decide how you show up is the two weeks Flowdonia spends settling what your differentiator is and what stands behind it. The work that follows makes it hold across everything the company does.