(Greatly condensed from the original, which you should read in its entirety; all emphasis in original.)
I like to think about media in terms of questions answered.
Like other media (the web) has a question that it answers better than any other. That question is:
Why wasn't I consulted?
“Why wasn't I consulted,” which I abbreviate as WWIC, is the fundamental question of the web. It is the rule from which other rules are derived. Humans have a fundamental need to be consulted, engaged, to exercise their knowledge (and thus power), and no other medium that came before has been able to tap into that as effectively.
WWIC is the thing people talk about when they talk about nicer-sounding things like “the wisdom of crowds” or “cognitive surplus.” It has become the first thing I think about when I think about the web. I start by asking: “How do we deal with the WWIC problem?” Everything else comes after.
The obvious example of WWIC at work is Wikipedia, created for free by unpaid labor. It tapped into the basic human need to be consulted and never looked back.
Once you see [thumbs-up/thumbs-down icons so that you can rank the comments], a website is complete. You're down to the bedrock. A boolean or integer value is the digital equivalent of a grunt. You can't get any more basic than a like, or a thumbs-up, or a favorite.