When you access a site on the Internet you download various components that make up the site. This may include blocks of text, pictures, and even interactive elements like quizzes for online course work. These components are saved in your web browsers cache so that they can be quickly used again if needed. A classic example is the title banner at the top of a webpage. If this rarely changes we do not need to waste time and bandwidth by downloading it every time we go to the site. However, when something goes wrong this mechanic can work against you. If your download is somehow not correct due to an error with the site or Internet connection you can save a non-functioning copy in your cache and your computer, not aware of the difference can continue to use this broken copy when you reload the page. To prevent this we clear the cached data and force a download form the website.