If you truly want your site to succeed in the search engines, a major part of your SEO strategy must focus on the importance of inbound links, or backlinks that come from an external Web sites to yours. The search engines expect people to link to pages they find to be of value. So, if no one ever links to your site SE’s make the assumption that it has no value to their users.
Google believes that calculating links and taking into consideration such things as what those links say, along with the quality of the Web sites they come from, is an effective way of determining a Web site’s authority.
Having relevant, reputable sites linking back to your site is one indication of its success and popularity in the eyes of the general online public. Backlinks do not only give the search engines a barometer of a site's popularity, they also aid in determining the topic, and relevance of a Web site in relation to its targeted keywords. Though the art of on-page SEO is, and will always be very important, gathering relevant backlinks is steadily increasing in importance.