Google results and how people respond to them.
The image above displays results for only one page for Google - the first page. The X-axis (along the bottom) lists the result in the order it appears on on Google's first page. The Y-axis (along the side), displays the percentage of people that click on a result once they've entered a search query in Google. Of the 1.2 trillion searches than occur each year, 396 billion clicks are made on the first result.
The staggering truth to this graph is not only the percentage of clicks the first result gets, but that by the end Google's 1st page, less than 6% or searchers go on to page 2.
This is why the competition is so fierce.