1. The feeling you get when an obscure writer or band that you like becomes popular because their book gets made into a big movie or their song is in a commercial and it leaves you all disgruntled because you knew about them way back when.
2. Feeling similar to the above caused by the sudden surge in the popularity of a certain person or entity.
Literal meaning (German): Sadness stemming from original loyalty
The grundtreuentraurigkeit was too much for Bob to take when he read that the Go!Team would be playing the Superbowl halftime show.