Unpleasant facts from within the Tibetan community, easily forgotten. A film documentation of historical importance:

For centuries the deity Dorje Shugden has been worshipped by the greatest and most important Buddhist masters, many of whom are among the most respected ones in the whole of Tibetan history. Also by the Dalai Lama's teacher Kyabje Trijang Dorje Chang.
If the Dalai Lama thinks that all the great masters were mistaken, he also denies them their qualification. Then the others would not be great masters.
Question: All the great masters who have worshipped the deity for centuries, were they all wrong?
Dalai Lama: "Wrong! Yes, wrong!"

The Dalai Lamas criticism and defamation of his own Root Guru created the schism of the Gelug order of Tibetan Buddhism and conflicts within the Tibetan community.

Documentation from January 5th, 1998 Part 1