Effective writing stays focused on one topic at a time. Do you know that Incan pottery never showed the human form? It used a variety of geometric patterns to create artefacts that had both practical and ceremonial uses.
The paragraph you just read should confuse you.
When you read it, you have no idea how it fits together. How does the idea that effective writing takes up one topic at a time connect to the information about Incan pottery?
If you were confused—and maybe a little frustrated–when you read the first paragraph, remember that feeling.
It can be an important tool in making your writing better.