Why do lamas reincarnate and what happens when they do?

When the lama dies, he does not want to abandon his students. So to continue this relationship between students and teachers, lamas come back. That is how the system or reincarnate lamas happen.

When a lama passes away, his student try to find his

reincarnation in many ways. Then this young reincarnate lama continues to work with his students from his past life as his own students, sometimes, also even their reincarnations as his students. 

And so this kind of life-after-life continuation of teacher student relationship, that kind of special system is something unique that comes from the lineage of the Karmapas. This connection is something that continues uninterrupted even by death.

HH, 17^th Karmapa
Ogyen Trinley Dorje

From Kamashila
Short-Ngon-dro teaching
Germany, 2014