The great thing about the Internet and the World Wide Web is it makes everything accessible to everyone. The difficulty is the everything and everyone bit. Unless you’re constantly on top of your content and updating your site, your competitors certainly will be, most likely. Then there is Google and the other search engines tweaking their algorithms and filtering what content works. The simple answer is to have a constant eye on your rankings and those of your competitors and products. The market is moving and changing your site has to adapt to survive. SEO is about staying head of the competition and attracting their customers to your site.