Links or Content? Nope, Attention
When you have a new idea can you spread it? You can do the most amazing thing in the world that would alter the course of history, but if you have no attention it goes nowhere. Days / months / years later somebody comes by and steals / repackages / reformats / relaunches your idea and is hailed a brilliant futurist. You wait in line for their autograph, and can do nothing but laugh or cry because you know you already published that idea, but unfortunately you did it at the wrong place or wrong time or you used the wrong headline.
An old site that already ranks well can see self reinforcing links for years until someone launches a better idea and owns that idea. But if ignored eventually someone will take the idea from you. If you do not have enough attention you do not have the margins needed to be sustainable and fight off competition. If you run a network without adequate attention it turns to spam.
A profitable SEO running a sustainable longterm website is an attention whore. They learn how ideas spread, what types of ideas spread, and how to format them to help them spread. They tap into the human ego and dig deep into psychology to help others want to help them. Marketers spread lies if the payout is high enough. Other times people accidentally spread inaccuracies, but that works too because people talking about it grants you more authority and reading the feedback forces you to learn more.
Some marketers are conservative and like to quietly build links and attention over time. Others like to see their name on the front page of the newspaper or Digg. Both ways work, but links are just a proxy for conversation and attention. Search engines follow people.
Once you have attention you can do whatever you want. Who cares if 90% of your ideas fail? You learn from every failure, content can easily be reformatted, and other good ideas come out of remains of past failures. You only need 1 to be really successful to be set for life. And if you keep trying to launch innovative valuable ideas then people are going to keep talking about you until you launch a success. And when it launches people will talk about it because you already have their attention.