When La La Land hits cinemas in December, it will mark the third time Ryan Gosling and Emma Stone have, right before our eyes, been the coolest couple who've never actually been together.We watched them in Crazy, Stupid, Love . We watched... okay, we watched the trailer for Gangster Squad and decided to pass, but still! Ahead of La La Land's premiere, we need to know how these two friends maintain such uncanny chemistry.Glenn Ficarra, co-director of Crazy, Stupid, Love, spoke to Entertainment Weekly about why Gosling and Stone have such a unique appeal.According to Ficarra, many actresses who read for Stone's role in the 2011 film were too intimidated by Gosling to be playful. "Ryan walked in, immediately flubbed his first line, " Ficarra told EW. "And [Stone] just laid into him, like, ‘Oh, you’re killing this buddy.’ She was the only one not to be intimidated by him, and in that moment John and I knew, ‘Alright this is it, she’s right for the part.’ She continued that, and they just got along really well. They have a very similar sense of humour...they riff off each other really well."Ficarra's theory about why the pair works so well together on screen? Their friendship and shared sense of humour run deep."They love each other in real life, and they get on like a house on fire," he told EW. "It wasn’t a lot of heavy lifting on our part. It’s making a move to hire the right chemistry."