I believe, if you were to ask any creative writer (professional or amateur), the one thing they want to get perfect when creating a story, is dialogue.
In my experience, when it comes to writing scripts, dialogue is easier to write. Okay, maybe not easier, but I can come up with dialogue way easier than an action scene. Now don't get me wrong, I do tend to trip up once in a while when coming up with dialogue for my characters, but 9 times out of 10, my scenes, my stories come from the dialogue I've developed. I have a better idea of what my characters will say then me coming up with an action sequence.
I think what makes writing dialogue difficult for most writers is the idea of making the characters sound natural. Heck, that's what I attempt to do in my writing, but while watching movies or television shows you see that's not really possible. Take the cafe scene between Ken (played by Brendan Gleeson) and Harry (played by Ralph Fiennes) in the movie In Bruges for instance. In their conversation about dealing with Ray (played by Colin Farrell), the conversation is very eccentric and fast-paced. Ken, is caring and knowledgeable but with a deadpanned matter-of-fact voice, while Harry is very loud and temperamental. While watching this scene, no one really talks the way they do. Their conversation is a bit of a roller coaster. Typically in the real world, a persons' conversation tends to stay in one mood (assuming the conversation doesn't last more than ten minutes), but their dialogue is a dance. That's what is being portrayed on screen.
The point of a dialogue is to sell an emotion. To tell a story. It's poetry in a way. That is why as an audience we are able to recount word by word some of our favorite lines from movies. So instead of searching for some secret recipe for writing that perfect dialogue, we should focus on what works for our story.