Blockchains address this problem in two ways. First, they enforce a complete ordering on all transactions, which generates a tree of alternative views of history. Second, they define canon for histories, along with a fork-choice rule that selects the canonical branch from the tree of histories.

Almost every social network of note had an early signature proof of work hurdle. For Facebook it was posting some witty text-based status update. For Instagram, it was posting an interesting square photo. For Vine, an entertaining 6-second video. For Twitter, it was writing an amusing bit of text of 140 characters or fewer. Pinterest? Pinning a compelling photo. You can likely derive the proof of work for other networks like Quora and Reddit and Twitch and so on. Successful social networks don't pose trick questions at the start, it’s usually clear what they want from you.

Ohhh, never thought of this hypothesis: that the act of getting drunk together might be a social technology that helps us verify the trustworthiness of others by inhibiting their higher cognitive functions and thus making it harder to consciously fake things.