Before I started writing thrillers, I tried writing in other genre's. All genre's are not the same. While it's true all writers need to have an affinity for story. different genre's demand their pound of flesh in different ways. Romance requires an author to be able to translate the subtleties of human emotions, non fiction requires a person to see the mundane and discover new and thriller requires us to take something we think we know and present it in such a way we want to know about it all over again.
To all of us that are brave enough to pick up the proverbial pen, and then publish our work to the masses. congratulations on being your own Subject Matter Expert.