Natural Monopoly Law

The mechanism behind the Natural Monopoly Law is rooted in the statistical distribution of purchasing behavior, specifically the negative binomial distribution (NBD) and the Dirichlet model. In any given category, the vast majority of consumers are light buyers - people who purchase from the category only once or twice a year.

Mathematically, as a brand's market share increases, its penetration must increase. However, the pool of heavy buyers in a category is finite and usually already saturated by multiple brands (Repertoire Buying Behaviour). Therefore, for a brand to achieve significant market share, it has no choice but to recruit from the much larger pool of light buyers.

There is also a psychological and physical availability component. Large brands have higher Mental Availability (they are the first to come to mind) and Physical Availability (they are everywhere). Light buyers, who put very little cognitive effort into their purchases, are more likely to choose the most prominent, easily accessible brand. They don't have the motivation to seek out niche alternatives. Conversely, smaller brands lack the reach to be noticed by light buyers, leaving them with only the heavy buyers who are more category-involved, more likely to seek out variety, and more likely to be aware of smaller players. Thus, the smaller brand is monopolized by the heavy users, while the large brand enjoys a natural monopoly over the light users who represent the bulk of the market's potential growth.