Why is three positive conference reviews more reassuring than one thousand facebook comments?

How do I know the reviewers are experts? I don't know who they are. I know the context and background of my facebook friends, I can critically interpret their replies. The reviewers are anonymous. They're people who had some time, just barely, probably during a commute or on the toilet. Or who owed someone a favour.

I've reviewed papers, usually having been asked to by the person who was supposed to be reviewing, about topics I barely know. I think: "it's okay, the other reviewers will swing it if I'm wrong."

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