Donick Cary talks to Cody Brotter about being\xa0David Letterman's Head Writer at age 25 before leaving to write for "The Simpsons"\xa0(which won him an Emmy Award), writing on shows like "Parks and Recreation,"\xa0"New Girl," "A.P. Bio," and "Silicon Valley," as well as directing a documentary about psychedelics (after being inspired by a conversation he had with\xa0Ben Stiller).