Being sincere is a matter of being present in your work. The more present you are, the more sincere your work will be. And, in my opinion, the most sincere work you ever produce will be the best work you ever produce. In a certain light, writing could be considered the pursuit of utter-sincerity.
My goal is to have a clear sincerity in everything I do. I try to eliminate as much as possible in between my brain and the activity at hand. To do this, a writer must know what not to include in their writing. We do this by knowing what is implied in our work.
Every person, place, trauma, thought... Every single experience you have ever had is implied in your writing. That's your style. That's your uniqueness. That's your sincerity. Being truly sincere is being all of those things at one exact moment in time, and then creating a thought, a sentence, and so forth. There is no need to deliberately spend time considering those things, wondering how they will present themselves. They are already there. Implied. Knowing what's implied is an absolute necessity when being sincere. Explicitly stating what has already been implied is redundancy.
Sincerity is a way of writing. That may seem trite, but it's true. It's a mindset. It's the vehicle you use to transfer thoughts from your brain to your pen. It goes well beyond words, but it shows in the words. Audiences read, but more importantly, they infer.
What I'm talking about here is not a sincerity in the information provided in a written piece. It's not an accuracy of facts provided, or direct beliefs instilled in words by a writer. It's what leads us to write. It's the filter that we run information through to even begin writing. It is us. It is the writer. It is the work.
In any creative world, and especially in writing, you will find vast amounts of artists/writers that produce seemingly identical work. That is because they lack sincerity. As sincerity rises, our work becomes more different, more unique, and more specifically true. The most unique and spectacular artists of our time worked with deep sincerity in creating their work. Devoid of influence. Without conforming, succumbing, etc. What they wrote was truly them.
Perhaps the greatest case study for sincerity in writing is Ernest Hemingway. A man that could write fiction with more sincerity than most could write an autobiography. As I've gotten older, I have come to appreciate Hemingway more and more for his style of writing. A style so natural, that it's too natural. A style so natural, it's unnatural.
The only thing that is implied in Hemingway's writing is himself. Nothing else. That's not to say that he, himself, is present in the plot, it's merely to say that his human existence is present in the way that he connects to the audience. Crystal clear sincerity. He does not distort the information in any way.
Hemingway has the ability to say so much while writing so little. His account of the plot tells exactly what is happening, and nothing more. He gives the reader a story in it's truest form. Some authors are great because of their outlandish creativity and story-telling abilities. Hemingway is great because of his pure writing style. The pure writing is what makes the story happen. Nothing is implied; everything written is crucial. Each sentence is something that happens. Each sentence is it's own event. Hemingway writes novels with more stand-alone sentences than any other writer I've ever seen. He uses a magnitude of incremental events that sum to a more grand conclusion, whereas other writers contribute multiple sentences to one event, with a more calculated climactic push. Premeditated decisions could allow a writer to control where the reader's focus lies. Hemingway was able to drive the audience in a specific direction without ever explicitly pointing them in that direction. What's most astonishing, is his ability to present such little information to readers, yet have them all come to the same conclusion. Truly astonishing, and truly masterful.
Someone who has not read Hemingway might read this and think his work sounds bland or monotone. It's not, because it's sincere. At no point did Ernest Hemingway think about writing a story the way anyone else would. He had one way of presenting beautiful creativity to the world, and that's what he did. He stayed out of his own way, which, in many cases, is the root of sincerity.
To consider what actually exists in the plots of Hemingway novels is not to consider much, but there is a reason why his work has lasted with such prevalence. His artistic magnitude can be attributed to a unique and dark power presented in his writing. That dark and simple power in his writing, is not his writing style, but instead is his existing style. The way he writes is the way he exists; and his ability to show that to an audience proves his sincerity. Ernest Hemingway is first, a master of sincerity, and second, a masterful writer.
The most difficult part of being sincere, is that there is no writer to study to help you find your most sincere form. There has never been another you. What you are is what your writing should be. Your writing should be you molded into a work of art. You in a novel. You in a poem. You in a painting. You in a song. You. Ernest was Ernest, and you should be you. Sincerity is nothing other than your most honest and true human existence. Take that existence, pour it onto paper, and only then start writing.