Families

All families are cults, strange islands, and dictatorships to some degree.

All happy families are alike; every unhappy family is unhappy in its
own way.
— Leo Tolstoy, Anna Karenina

Anna Karenina principle
From Wikipedia

The Anna Karenina principle describes an endeavor in which a deficiency in any one of a number of factors dooms it to failure. Consequently, a successful endeavor (subject to this principle) is one where every possible deficiency has been avoided.

The name of the principle derives from Leo Tolstoy's book Anna Karenina, which begins:

Happy families are all alike; every unhappy family is unhappy in its own way.

In statistics, the term Anna Karenina principle is used to describe significance tests: there are any number of ways in which a dataset may violate the null hypothesis and only one in which all the assumptions are satisfied.

Example: failed domestication

The Anna Karenina principle was popularized by Jared Diamond in his book Guns, Germs and Steel. Diamond uses this principle to illustrate why so few wild animals have been successfully domesticated throughout history, as a deficiency in any one of a great number of factors can render a species undomesticable. Therefore all successfully domesticated species are not so because of a particular positive trait, but because of a lack of any number of possible negative traits.

From chapter 9 of Guns, Germs and Steel, six groups of reasons for failed domestication of animals are:

* Diet - To be a candidate for domestication, a species must be easy to feed. Finicky eaters make poor candidates. Non-finicky omnivores make the best candidates.
* Growth Rate - The animal must grow fast enough to be economically feasible. Elephant farmers, for example, would wait perhaps 12 years for their herd to reach adult size.
* Problems of Captive Breeding - The species must breed well in captivity. Species having mating rituals prohibiting breeding in a farm-like environment make poor candidates for domestication. These rituals could include the need for privacy or long, protracted mating chases.
* Nasty Disposition - Some species are too mean and nasty to be good candidates for domestication. Farmers must not be at risk of life or injury every time they enter the animal pen. The zebra is of special note in the book, as it was recognized by local cultures and Europeans alike as extremely valuable and useful to domesticate, but it proved impossible to tame. Horses in Africa proved to be susceptible to disease and attack by a wide variety of animals, while the very characteristics that made the zebra hardy and survivable in the harsh environment of Africa also made it fiercely independent.
* Tendency to Panic - Species are genetically predisposed to react to danger in different ways. A species that immediately takes flight is a poor candidate for domestication. A species that freezes, or mingles with the herd for cover in the face of danger, is a good candidate. Deer in North America have proven almost impossible to domesticate and have difficulty breeding in captivity. Horses, however, immediately thrived from the time they were introduced to North America in the 17th century.
* Social Structure - Species of lone, independent animals make poor candidates. A species that has a strong, well defined social hierarchy is more likely to be domesticated. A species that can imprint on a human as the head of the hierarchy is best. Different social groups must also be tolerant of one another.

Ecological risk assessment

Moore describes applications of the Anna Karenina principle in ecology:

Successful ecological risk assessments are all alike; every unsuccessful ecological risk assessment fails in its own way. Tolstoy posited a similar analogy in his novel Anna Karenina : "Happy families are all alike; every unhappy family is unhappy in its own way." By that, Tolstoy meant that for a marriage to be happy, it had to succeed in several key aspects. Failure on even one of these aspects, and the marriage is doomed . . . the Anna Karenina principle also applies to ecological risk assessments involving multiple stressors.