Here's why:
* Clarity: Placing it first sets the reader's expectations and guides them through the paragraph's focus.
* Organization: It acts like a roadmap, clearly stating the main point the paragraph will explore.
* Flow: It naturally transitions into the supporting details that follow.
However, sometimes the topic sentence can be found in other locations:
* End of the paragraph: This is less common but can be effective for building suspense or emphasizing a point.
* Implied topic sentence: Sometimes the main idea isn't explicitly stated but is understood through the supporting details.
Ultimately, the best placement depends on the writer's style and the overall message they want to convey.