The mistakes described in this article that are made by developers and designers are the reason for a high bounce rate. A bounce rate is calculated by how many people visit a site, against how many people click off the site, close the tab, close the window, or press back within a ten second time period. A high bounce rate means that people are looking at your site and then not looking at it (bouncing on and off again). The first four mistakes are those that web designers make. They are silly mistakes that show a lack of forethought, testing and research. The rest of the mistakes are those made by developers. The developers are the people who take an already established design/website and add things to it.