Why is my fist novel so hard? It's not an unreasonable question and you're not foolish for asking. Anyone who wants to write a full-length book manuscript is in for an uphill battle without much sympathy or understanding from your fellow human beings who don't put words on paper.
The fact is that most of us are not trained for this line of "work," even though we tend to do it as a hobby or during what passes for spare time. That aspect of a writer's challenge is--by itself--a lot to unpack. Those few who trained for it have been through many hours of classroom study, they've read a wide variety of subjects--and--may possibly do some form of writing as part of their "day job."
It's tough to overcome what you don't know. You'll spend a lot of time learning what you never needed to know...until now. Think of any book you want to write as a process. Knowing what the big-picture steps are goes a long way towards understanding the little things. It's not enough to knowing the basics about your story, you've got to know things about your characters and plot that explain, make, or justify the end. Tackle that before you start noodling your outline.
Knowing how it starts and ends makes it easier to describe your Good Guys and the Bad Guys. Everybody likes a worthy villain. Grinding through an outline of your story forces you to think. Sometimes, the book doesn't end like we think it...was going to, before I wrote the--you get my point.
Yeah, been there and done it.
Grammar, spelling, and punctuation are just part of the recipe that makes a story easy or hard to read. There's a little bit of theater involved in what you do, as you tell your story. No matter what genre, all characters (Good or Bad) are in places while they say and do "stuff." If you don't write the words on to a page, those things don't exist. They never happened. They do happen just as you write them,
completely or in broken parts.
If there is any "secret sauce" to a novel, it would the all the little transitions that indicate somebody is doing something, saying something, or about to. All of them lead to outcomes which are the result of what somebody said or did. Dialogue is a back-and-forth situation, somebody says and somebody replies. Gun battles and car chases are more complex and often bloody, even so--they are still happening because somebody is doing something and the other guy is reaction to it. Even if they are just reloading.
There are fancy names for all that, none of which mean anything to you if you never had a reason to know what they were be-fore you decided to write that first novel. If there is any one specific thing to remember, it's this: What you learn from doing this stays with you. What you think of as a mistake here and now becomes skill later on--when you don't do that again. Your first book is a lot like learning on the job. It's not any fun while you're doing it, but still useful to talk about years later.
I am serious. Think of your first novel as a form of learning experience. In truth, many of today's famous writers--the acknowledged masters of their craft--did not write flawless first novels. Experience allowed them to get better over time, even when they had classroom training. There is no requirement to publish what you wrote, either. I killed and buried three manuscripts to learn what I needed to know before coming at this the way I do now. Be patient and learn sliwly over time,
the rest quite oftem takes care of itself.