They say you should write what you know, but how is that possible? If we only wrote about our experiences, most of us could only tell one story. It might not seem necessary to you; after all, Tolkien never went to Middle Earth, I'm not a Roman, and Stephen King has never been attacked by a madman with an ax.
Donald Maass says you shouldn't write what you know, but write what you care about. Passion is all you need.
He makes a good point, but I agree with the rule of sticking to what you know. I believe most writers who shudder at this idea just don't know how to apply it.
I've read stuff and thought to myself, "She has no idea what she's talking about." The characters' feelings and actions feel false, forced, and contrived. I especially feel this way when people write about depression. Having seen a lot of it in my life, it's easy to tell what's genuine and what's not.
Here's an example; J.K. Rowling has never been attacked by a dementor. However, she has struggled with depression. Dementors are creatures who suck the happiness out of you, making you feel as if all the light has gone out of the world. She's pulling from her own experiences. It resonates with readers because she's writing what she knows.
In my WIP Fierce, one of the main characters gets raped. (I feel like such a sell-out; it's seems half the books in this world have rape victims in them.) I myself have never been molested. I refuse to write the scene of it actually happening because I feel it would be presumptuous -- even disrespectful -- for me to attempt to describe it.
However, I do have some experience with trauma. I once got hit by a car while riding my bicycle and shattered the windshield with my body. The post-traumatic stress was terrible... I was deathly afraid of cars for a year!
Ergo, I started my novel not with her getting attacked, but with her at home the next day trying to hide the rape from her husband. It's difficult because she jumps at every sound. She can't stop shaking. Whenever he moves his hands too close to her, she flinches. All she wants to do is hide in her bed under the covers.
This experience is real to me, and my critique partners say it feels real in the text. I wrote what I know.
I challenge you to look at your writing and ask yourself how your character's struggles relate to your life. The character doesn't have to be you, but surely you can find some common ground. If you can put pieces of yourself in the writing, it will be potent.