Writing is a process through which you begin to understand your subject better. But that doesn't mean that you don't need to spend a little time trying to organize your thoughts first.
This is especially so when you're trying to figure out what to do with a literature review. Commonly I speak with people who can't get their literature review right because they're spending their time reading article after article, and always saying that they can't figure out what to write because they need to read another article. That's not how it works.
You have to start with trying to explain what your idea is--that's the point in writing anyway, to show what your ideas are--even in a literature review chapter.
If you take time to set your ideas down--write an outline, or an abstract, of the main ideas that you want to express--then when you write, you write with a purpose. As a result your writing has coherence, direction and focus.
If you do not set your main ideas down, but instead try to write some abstract general discussion of your general topic, then you lose focus and you lose direction. Instead of writing to your own purpose, you end up trying to sequentially report on one study after another. And every study that seems good needs to be included, and there's no clear boundary on what level of detail is necessary. Thereby you lose coherence, direction and focus.
If you have a plan for what is important to you, then relevance to your specific project is a very clear guide to which studies are discussed in detail and which can be passed over in a sentence.
Literature reviews are perhaps the worst trap if you haven't taken time to organize your thoughts and make a plan for what you think is important. In a literature review chapter you're supposed to be showing familiarity with the general literature on your subject--but in reading different studies, you can end up following the ideas of those studies if you don't already have your own set purpose. And that's a problem because usually each study has its own point of view, so if you're following, you flit from idea to idea. Only by trying to commit to your own understanding and explanation of the ideas, do you get to settle on the one view that gives coherence to you work. And then, the whole academic discourse takes a new shape in the context of your own personal perspective, and your personal perspective then takes shape as you test it against the other ideas in the literature.
So organize your thoughts first, then write about what other people have written.