Top-down vs. bottom-up writing processes
Most writing advice assumes you already know what you want to say. Start with the outline, abstract, or some other structured template. These are all top-down strategies: define the structure, then fill it in.
This work well if you already have a rough idea of where your paper is going and what your conclusions are going to be. However, I often see that novice scientific writers don’t know these clearly yet. They discover them through the writing process (see: “Writing for yourself” in What is writing). In these cases, a bottom-up approach often works better: start by building the content of the paper (including the conclusions), then reverse outline to build the structure afterwards.
Most writers mix both approaches
In practice, most writers don’t work purely in linear direction top-down or bottom-up. Most writing processes are a mix of the two, either leaning more towards top-down (if you already know what you want to write) or more bottom-up (if you need to discover more first). You write some stuff, then change the structure, or maybe work from a provisional outline. It’s all fine. It’s just important be aware of what you’re doing (see also: What is writing).
Why bottom-up suits novice writers
This hub assumes you’re relatively new to both (1) your topic and (2) the journal article format. That means you have more new information to hold in working memory than an experienced writer — so writing things down first lets the text itself become an extension of your memory.
It also means starting with an outline is harder than it sounds: you’d be imposing a structure using a format you’re not yet deeply familiar with. Getting the content down first, then structuring it, is simply less cognitively demanding.
Getting started with writing? The suggested workflow lists the bottom-up process step-by-step.