Category Entry Points
The set of situations, needs and moments in which a buyer thinks of a category — the cues a brand must be linked to in memory to be considered at all.
Breaks when Useless when the category does not yet exist — a genuinely new product has no moment to be recalled in, and must build one before this tool has anything to work on.
Double Jeopardy
The empirical regularity that brands with smaller market share have both fewer buyers and slightly lower loyalty among the buyers they have.
Breaks when Weakens where switching is contractually locked (telco, insurance) and in heavy B2B where the buyer universe is structurally small.
NBD-Dirichlet
A stochastic model that predicts, from category structure alone, every brand's expected penetration, purchase frequency and buyer overlap.
Breaks when Assumptions fail with few players, high involvement, or one-off purchases. It also tells you nothing about why a deviation exists.
Jobs to Be Done
A method that defines demand by the progress a customer is trying to make, rather than by product category or customer profile.
Breaks when In low-involvement, habitual purchases it degenerates into inventing a job that was never there. Not every purchase has a purpose behind it.
Mental & Physical Availability
A two-factor account of brand growth: the probability of being noticed or recalled in a buying situation, and the ease of buying once you are.
Breaks when Where distribution is fixed and single-channel, the second term carries no information and everything collapses into the first.
Diffusion of Innovations
An account of how an innovation spreads through a population over time, and of the innovation attributes that set the rate.
Breaks when Strong at explaining backwards, weak at predicting forwards. You only know who the early adopters were afterwards.
Crossing the Chasm
The claim that a discontinuity in buying logic separates early adopters from the early majority, crossed by dominating one narrow beachhead first.
Breaks when No empirical support for the chasm itself. Outside B2B technology the mechanism has little to stand on — the focus advice is good, the theory under it is not.
TAM / SAM / SOM
A three-layer market sizing convention: the total market, the portion a given business model can serve, and the share it could realistically win.
Breaks when Produces no decision. The number is almost always reverse-engineered from the desired conclusion, and it never identifies which assumption is the fragile one.
Segmentation & Targeting
Dividing a market into groups expected to behave differently, then choosing which of those groups to serve.
Breaks when It breaks as a description of who buys. Competing brands within a category are repeatedly measured as having near-identical buyer profiles: the segments differ in size, not in kind. A segmentation that assigns each brand its own distinct demographic or attitudinal buyer is describing a market that measurement does not find. It survives as a targeting and media convenience, not as a theory of demand.
Buyer Personas
A composite fictional buyer — name, age, role, frustrations — built so a team has a concrete person to design and write for.
Breaks when It breaks the moment the fiction is treated as evidence. Personas are typically built from a handful of interviews and then used to exclude — this campaign is not for her, that channel is not where he is. Because competing brands largely share the same buyers, a persona used to exclude is excluding people who already buy from you. The failure is silent: nobody audits the customers a persona quietly wrote off.
The 95-5 Rule
The proposition that at any given moment roughly 95% of business buyers are not in the market, so most advertising has to work by being remembered later rather than by converting now.
Breaks when The 95/5 split is a derived estimate, not a measurement. It comes from average purchase-cycle length: divide the share of buyers who transact in a year by the length of the cycle and you get the in-market proportion. In categories with short cycles, high growth, or frequent re-purchase, the in-market share is materially higher and the rule under-invests in capture. It is a reminder of proportion, not a constant.
The Starving Crowd
The heuristic that the greatest advantage in any business is an audience already desperate to buy, so demand should be chosen before the product.
Breaks when Visible demand is the most contested resource there is. A crowd everyone can see is a crowd everyone is already selling to, so the heuristic routes founders straight at the categories with the highest acquisition costs and the most entrenched incumbents. It also carries no test — nothing in it distinguishes a starving crowd from a well-fed one until the money has been spent finding out.