It's called The Anna Karenina principle. Tolstoy posited an analogy in his novel Anna Karenina that "happy families are all alike; every unhappy family is unhap

It's called The Anna Karenina principle. Tolstoy posited an analogy in his novel Anna Karenina that "happy families are all alike; every unhappy family is unhappy in its own way." Interestingly, Peter Thiel starts his book Zero To One with a reference to the Anna Karenina principle by showing a corollary in business: "All happy companies are different, all unhappy companies are alike."