Most writers feel obligated or attached to a particular genre when sitting down to write. This makes perfect sense, as this is how the publishing industry is designed. Readers tend to be drawn to particular genres, therefore straying away from your chosen genre is to abandon a preset readership, or so it seems. I maintain that the greatest novels naturally cross over into other genres, even if for only a few pages.
This is a reflection of life, in fact. No one's life story sticks to one particular genre without deviating occasionally. Life exposes you to horror, love, comedy, mystery, and perhaps even a bit of science fiction. And what is storytelling if not a way to express the truths in life?
As the old adage goes, "write what you know." Most people seem to take this as though "what you know" has to stem from your own personal experience. This is not true. Take any fantasy writer, for instance. Do you think they have actual hands-on experience with wizards, elves, and magic? Sadly, the answer is no. So where does that experience come from? The answer: reading and exposure.
So let's say, for the sake of example, you tend to write fantasy. This means that you must be a fan of fantasy literature and are perhaps well-versed in the genre. Maybe you can name more fantasy authors than you can types of food. While this is great and terrific experience, if you dig deeper into your favorite fantasy stories, you will find bits and pieces of other genres inside.
Is there a love interest? A horrible beast? Is there death? Are there parts that make you laugh? Is there drama?
These are all pieces of other types of literature that have made their way into your favorite book. If you take a magnifying glass to each page, you will quickly realize that your favorite fantasy book is also a great work of comedy, horror, drama, romance, and so on.
This is why it is important to branch out and practice in more than one genre. Having your story confined to a singular genre makes it a specialty, and that's okay. But what about the inevitable scenes that will touch on action/subjects belonging to another specialty?
It is important to read and write in genres outside of your comfort zone. There are specialists out there, and you should not be afraid to pick their brains. If you write horror, read a Nicholas Sparks book sometime. Why not? He obviously has a good handle on what makes a love story enjoyable to millions, so there's something to learn there. Take something from it and apply it to your horror story. If you write about a couple in love and make their relationship believable to the reader, then it will be all the more horrific should, you know, anything bad happen to them...
And the street runs both ways. If you enjoy writing love stories, then perhaps pick up a Stephen King book. He is a master of tense and gruesome tales. Maybe something horrifying will happen to your main characters in one of your stories that will create the conflict that threatens their love.
What's the worst that can happen? At the very least, you will learn more about what you don't like about a particular genre and reinforce your belonging to your genre of choice.
I'm not claiming to be the master of writing literature that crosses genres in any way, shape, or form. In fact, I learned and am still learning this lesson the hard way. During the process of editing my science fiction novel (a process I am currently engaged in), I found that the scenes I wanted to be horrific were missing something essential: horror. My own solution was three fold: 1) I started reading horror stories, 2) I wrote a short horror story, and 3) I entered that horror story into a contest where I could engage with horror writers. I have learned an immense amount about horror that I would have otherwise abandoned had I not stepped outside of my comfort zone. Now, I have a short horror story, a broadened network of fellow authors, and a better grasp of what makes a story horrific. Learning this lesson would have taken much more time to learn if I had restricted my exposure to science fiction.
Reading and writing fiction should be limitless. If you enjoy a particular genre, then that is a wonderful place to be. But for the sake of the characters, conflicts, plots, and worlds you create, tear down the borders and expand your potential by tackling stories outside of your comfort zone. It will only make you better as a writer. Write what you know, but don't forget to seek out more to know as often as possible.
An exploration of weird sub-genres:
A neat little video on Medium Vs. Genre:
35 Genres and other varieties of fiction: http://www.dailywritingtips.com/35-genres-and-other-varieties-of-fiction/
A list of writing genres: https://en.wikipedia.org/wiki/List_of_writing_genres