If your topic is too broad, you will be swamped with information, making it hard to sift through it all, organize it, and cover any aspect of it in detail. You will have to
You would be overwhelmed with information if you chose a broad topic, like computers. Focusing on the Internet though, cuts the number of results drastically, but it is still a pretty broad topic. Investigating the use of the Internet in education, however, makes your topic more manageable, and researching a specific type of education, such as online education, narrows your topic even more.
Compare these results.
The above examples use the Boolean connector AND to narrow the topic.