It is unusual, according to former intelligence officials, for U.S. spies to be identified and even rarer for them to be publicly shamed.

WSJ: Russia Expels U.S. Diplomat

Albino individuals of adult frogs, toads and newts are considered to be very rare and cases of multiple albinistic individuals in a breeding population are even rarer.

BBC: 'Rare' albino tadpoles uncovered

It must be said that successful partnerships are rather rarer than failed ones: business people tend to be alpha types, and money and fame can destroy even the solidest friendships.

ECONOMIST: Schumpeter