The inciting incident that sparks The Silmarillion and begins pretty much everything that influences the entire future of Middle-Earth. Fëanor grows up to be an influential (and a bit of a jerk) character and creates the powerful jewels known as "The Silarmils". With these jewels comes a whole knew mess of troubles, as well as the return of Melkor!
If you've ever wondered how or why the events of "The Lord of the Rings" played out the way they did, this is it in a nutshell.