A phenomenon, a mind condition related to all the long living races with limited brain capacity but brought up first by the dragons as they show it the brightest.
As the long liver reaches their brain's max capacity their consciousness starts to fade away because of memory rewriting that starts to happening, decaying and leaving only the strongest of memories that they get fixated on: those can be greed, violence, hatred or obsessive crave to protect something or someone.
The point of no-return highly depends on physical condition of subject, specifically their brain. The more information they consume over time the faster it happens. It made some of them to implement some techniques like meditation and information consuming limitations to prolong the life of their sentience.