One of the biggest advantages an author can have is to be trained as an actor.
We're talking the in-your-head, "Method," Marlin Brando style of acting, not the theatrical dramatic flourish style of acting. But, since the drama of a story goes on in the author's head, it winds up being extremely important.
"Method" acting calls for the actor to find the reality of what's happening in his or her head, and to carry that reality to the stage or screen. This absolutely has to be true for an author, trying to translate the characters' reality to the page (or, these days, screen.)
As the author, when the character is feeling pain, do you? If you do, the words you write will find a way to express the emotion on the page. If the character is joyous, are you? The readers will know through the words you write. When you write from loss, from pain, from ecstasy, readers can tell. It adds a layer of reality to the story, as well.
Of course, an author also has to be the director, telling the "camera" of the reader's mind where to look for the shot, letting the set designer and prop crew know what to have on the soundstage for the actors to use.
But the actor carries the play when it's actually performed. If what is happening to your characters is real in your head, it's real to the readers. The reasons may be obvious or subtle, but readers will perceive it. They will know. And emotion makes events more real than anything else.
Be a "Method" author. Get in your characters heads and hearts.