The long tail is an economic theory which details the financial viability of niche media products.

Niche films
Mongol- 2007 about Genghis khan
Flags of our fathers - 2006 American war against Japan
Letters from Iwo Jima - 2006 Japanese side of the war with America

The total Gross of all three films £161,000,000

The total gross of Harry potter and the philosophers stone £974,000,000

This shows that the theory of the long tail doesn't work as a mainstream market film made nearly 6 times the profit of three niche films.