Ten years ago, when Jimmy Wales put a few hundred stubs on a web platform to which anyone could write, and which anyone could edit, but no one was paid to do either of these, it was doomed to failure. Or so then-conventional wisdom would have said. Anyone who would have proposed that within five years Nature would claim that Wikipedia's science articles are not fundamentally worse than those of Britannica; or that by the end of a decade it would become the standard reference online would have been laughed out of the room. Wikipedia was impossible. So, by the way, were free or open source software, Yelp, or Tripadvisor. They were all impossible because the dominant model of human behavior said that we were all fundamentally self-interested, and that without systems to reward good behavior and punish or constrain bad behavior, human enterprise cannot flourish. Without law or markets, we would simply devolved to mutual shirking and abuse.
That, to me, is the biggest gift Wikipedia has given us; a way of looking at the world around us and seeing the possibility of effective human cooperation, on really complex, large projects, without relying on either market or government processes. It turns out that we are creative, social beings; we do what we think is fun, not only what is profitable; we do what we think is right and good, not only what we think advances our interests; and we are able to organize ourselves, even at very large scales, into coherent social enterprises. It's not easy; but it is possible, and it is part of who we are and can be. Together with free software, like Linux or Apache, Wikipedia has become the common symbol of the possibility of this kind of human cooperation. Whether we call it crowdsourcing or peer production, online cooperation or "doing it like Wikipedia," social production and exchange have become a solution space for a wide range of information production problems.