I believe both @MarkBaker and @R.Rengold make good points in their answers. I want to address and add to @MarkBaker's last point about "The plotter vs the pantser" and the vision:
Some (it seems) can't write till they have it. Other can only get it by writing.
Heads-up: Personal experience from here
Some may feel a need to plot out everything before 'feeling ready to write the actual story'. If you're new to writing, this may be a very natural way of responding to "the challenge of writing a novel" - I felt this way, and spent more than 2 years plotting and world-building before writing the actual story.
I thought I needed to plan out every detail of my story in advance: Who did what when (and why) with what consequences, what the characters were 'like', how they related to each other, and what role they played in the bigger picture, when and how I would reveal the "secret" (science) and the list goes on (for 23 pages of points and notes).
Note: my genre is philosophical science-fiction (philoscifi), so I may need more world-building in order for my work to make sense.
But it wasn't a story, it was a plot
- A story revolves around the characters.
- We need get to know the characters, in order to feel the "important" events in the story.
- The characters come alive when you write about them.
It wasn't until I started writing - randomly following the characters I had sketched out - that their personalities and the actual story emerged. I didn't know the characters at all until I had written a good deal, and I'm still learning about them.
Now, I may be fortunately lucky with the following, but nonetheless: I started out writing seemingly random scenarios as a means of introducing my characters to the reader. Oddly, I kept writing seemingly random scenes that could then later be connected to the plot-points that I found crucial for the plot. The amazing thing: I was now able to connect emotion to the crucial plot-points, because the characters were naturally placed in them.
Knowing the characters makes it much easier to plot out the events in a way where the plot points and the greater plot makes more sense.
At first, I thought that everything I wrote had to be (and was) worthy of the final print - it's not.
BUT, even if it's not in the final print, everything you write (or have written) will help you in getting to know the characters (and their story) and thus isn't wasted. Luckily, most of what you have written will probably seem great until you've written something even greater and or clearer - making it easier to edit out the unnecessary parts.
Sometimes, something written about the character is edited out, but can be used later to create an authentic scene at a more crucial point in the story.
I/you/we/one/some will probably have to edit some large parts of mythe writing that end up being superfluous the the story, but I've never heard of a novel written from start to finish without thorough editing.
I hope the general advice and input is clear from the experience as described above, and that it only helps motivate actual writing!