Objective of SEO
Basic objective of SEO Search Engine Optimization is to bring your own site in SEPR Search Engine Page Ranking as high as possible to the top in front of your competition and the only way to do that, is to have keywords rich content SE visitors will have affection, thus visit your site and to place backlinks to your content in natural way.
You can SEO only your own site
No one cans SEO Social, Articles and Directories sites because technically these sites out of SEO reach. You just cannot Search Engines Optimize site you personally don’t own but what you can do is to benefit your own site by using available media to Search Engines Marketing it.
Because you have no influence over somebody else actions and cannot control how others are running their sites you simply cannot SEO their sites to your like. If site owner decides to edit your article or to place nofollow tag or to remove hyperlink all together, there is nothing you can do about that and because of that you can only SEO your own site.
SEO – SEM confusion
SEM Search Engine Marketing is off page method of traffic building. Some people are using term SEO whereas in reality they mean SEM believing that these two are inseparable but the truth is, they both serve two different purposes.
If you place your article somewhere else but your own site, SE algo will pull that site (not your) to the top in SEPR and the only benefit you will get if you have had placed backlink in that article to your own site is visitors and that by definition is Marketing.
Simply put, you are Search Engine Marketing somebody else’s sites by providing your own content to these sites thus giving benefits edge of SEO to others and not to yourselves.