Of course, that's just as long as you know what's going to happen. The second you reach a scene that you just can't figure out, everything goes downhill. When you hit that glass wall in your brain where suddenly nothing wants to make sense anymore, or that technical detail you've been putting off dealing with because you'll figure it out when you get to it (oh wow you got to it time to figure it out), it gets a lot less fun.
And that's the hard part about first drafts. There's nothing more terrifying than a blank page when you have no idea what to put on it. I imagine that this is particularly difficult for writers who have already been published and have contracts and deadlines, and now have to think up something so they don't get in trouble. I have the luxury of just switching to a story where I do know what's going to happen next.
But then, of course, the first story just stagnates on paper, waiting for that fleeting spark of inspiration to strike the author, who ought to just sit down and muscle through it like a big kid because the poor story is waiting.
Eventually, a metaphorical kick in the pants usually comes along and the writer will finish the first draft. Sometimes this has to happen several times before the story can actually be finished. Some authors skip around and then write the other scenes later. I can't do that--I find if I don't make myself write in order, those scenes will never get written.
And then we come to the second draft. In some ways, draft two is easier: everything is already written out. There's no blank page demanding things you can't provide. In others ways, it's harder. Now you have to make it good.
I'm pretty lucky in this aspect. My first drafts aren't masterpieces by any stretch of the word, but they're generally pretty solid-- good enough that I'm comfortable posting rough drafts of fanfics, and can sometimes even get an A on a first draft essay. Unless my first draft is years old, I can generally read it over without wanting to gouge my eyes out. But other people don't have that.
It can be painful to reread. It has been painful. It will continue to be painful. You'll probably want to burn the first draft and start over, but you won't because it took so much work. So you'll cut out things left and right and add some of them back, but then cut them again. You'll agonize over the structure of a sentence and realize that you use the word 'fantastic' fifty times in the same chapter.
You will go over everything and make it better.
But the really painful part comes with the third draft. Once you've written the second draft, you're probably satisfied enough with your story that you're willing to let other people see it, and then you let them read it. Some of them will love it unconditionally. If they're getting any level of nookie from you, it's probably not safe to trust their opinion entirely. If they're your mother, or they're ten years old, same thing.
So you'll find a really close friend who likes to read or write and understands that not every word that comes out of your fingers is golden, and you'll ask them to read it. They will, and then they'll tell you things they liked. You'll listen.
But then they'll tell you things they don't like. And you'll want to die of embarrassment. You'll resent this friend and not speak to them for several weeks because that's your favorite scene they just told you you needed to rework, and they've just insulted you so badly they're dead to you. You'll go back to your comfort people and pout while they tell you you did a great job.
But you won't be able to get their advice out of your head. And you'll reread the scene five times and realize that maybe they were right. You'll start playing around with the scene in your head and trying to figure out what's wrong with it.
Eventually you'll suck it up and call your friend and ask what they'd recommend you do to make that scene better. They'll tell you. You'll still be mad, but you'll suck it up and start working on it.
And then, if you're lucky, you'll have something worth taking a look at.