Imagine you have a brand new site, with no visitors. It's hard to get ranked in the search engines because you have 0 links. And without link your website will not rank, therefor have no visitors. And in order to build organic links you need visitors.
So here is what you first do. You build links to your site. And after a while you will rank for the keyword you are targeting. Then you will have visitors. Those visitors will convert as an organic links. Of course not all visitors will link to your site, but let's say some of them will.
This means the more traffic you have the easier you'll rank. But wait ...
If this theory is true, how can a brand new website over rank an established one? Since the established one is ranked on 1st place and gets a lot of visitors, how can the brand new site beat the established one? Can some one explain, or confirm theory?