The plot is the framework of the story. It’s the structure upon which you build, insert characters, scenes and the like. You want to always keep the plot in the back of your mind so you can call it back when needed.
You’re thinking I’m not interested in a business. I just want to write and sell books. But surprise, that is a business! While writing can certainly be fun, it is for me, it can also be profitable. And for that reason alone you need to think of your writing career, no matter how many books that entails, as a business.