The hip in hip-hop is not an accidental adjective. The entire genre thrives on cool. Similar to its sister genre in pop music, the minute a specific hip-hop trend loses its allure, it's immediately cast out. Irrespective of how revered a seemingly immutable element of hip-hop appears, very few artists and trends have any real staying power. Consequently, anyone that can survive a decade in rap music and remain as relevant as they were in their prime exists as an enigma in the genre. Lil Wayne incepted the current wave of tattoo-clad rap artists and is as active as any modern rapper.
Even though there are a handful of timeless rap artists, few are as eternal as Dr. Dre. In the 80s, Dre helped bring gangsta rap into the mainstream. In the 90s, he brought us Snoop Dogg and Eminem. Nowadays, everybody wanna talk 'bout Kendrick Lamar and Symba being Dr. Dre's proteges, but how does Dre retain the ability to craft a hit?
In the video linked above, Symba explains Dr. Dre's writing process.