Writer's Block

There's something I really didn't get when I wrote Pure at Heart. I didn't get what Writer's Block was, and how it felt like. I don't know if it's just me, but I think that it's the case for all author's who were writing their debut novel in a series.
When I started Blazing Heart, I was so excited. I had a vivid vision of everything I wanted in the sequel. I started writing and writing, and there were many times where I just wanted to close my laptop shut and scream out in frustration. I would just sit their for minutes, trying to figure out what to write next. And I would write like three chapters, before I realize that I do not like what I just wrote. I would delete it, and start over, no matter how much I didn't want to. Now that I think of it, it might just be the fact that after you write a book, you realize that you want to change some things in it, except you can't--because its already published. So when you start writing another book, you think, "Oh, well, I don't want to make the same mistakes over again, so I'll just be really careful this time." Except, that results in you not writing anything at all.
I think I finally understand why writing a book usually takes years. I'm about 25,000 words in, and I think that I want to delete about ten thousand of them already. In fact, I have no idea where the plot is going--I'm just writing. I'm trying to get my thoughts down. This is the first time, I've tried something like this, and I hope it works. Yeah, I'm planning, but I think a real author plans, but also improvises when she writes. If she doesn't like a part of a plot, she should be able to change it, to the way she likes. And I think that's what's so amazing about being a writer. The fact that YOU get to change the story to what YOU want to be--not someone else. It's what makes writing so much different, and so much better than reading. You are in charge this time. There's no yelling at the book, drawling out, "Whyyyyy?" s anymore. There's no sulking over something that happened, and you didn't want it to. Writing expresses you.
So guys, when you have Writer's Block? Think of me. Sitting here. About to delete like half of her word count.