The Law Of Repertoire Buying

The mechanism behind repertoire buying is rooted in both cognitive psychology and statistical probability. Humans are cognitive misers; we don't want to spend precious mental energy evaluating every single option every time we buy toothpaste or cloud software. Instead, we develop a repertoire - a subset of brands we've tried and found acceptable.

Mathematically, this is explained by the Dirichlet model. The model assumes that: 1. Consumers have different long-run propensities to buy from the category (some buy often, some rarely). 2. Consumers have different long-run probabilities of choosing a specific brand within that category.

Crucially, these choices are independent of the previous purchase. If you bought Brand A last time, your probability of buying Brand B next time remains constant based on your long-term repertoire. This leads to polygamous loyalty. A consumer might buy Brand A 60% of the time, Brand B 30% of the time, and Brand C 10% of the time. They aren't switching in the sense of leaving Brand A; they are simply fulfilling their repertoire.

Psychologically, this is driven by Mental Availability. A brand enters the repertoire through distinctive assets and consistent memory building. Once in the repertoire, the specific choice at the shelf or screen is often determined by Physical Availability - is the brand there, and is it easy to buy? The Sole Loyalist (someone who buys only one brand) is almost always a Light Buyer of the category. They look loyal only because they've only made one purchase in the data window. As soon as they buy more frequently, they inevitably become repertoire buyers.