Over the last few years I've increasingly crossed paths with the following claim on the internet: "The average life expectancy for a fiat currency is 27 years." Is this claim true? What definitions are being used? I mean, are we talking about inconvertible paper money here, or currency that was convertible into gold, too? I finally got curious enough that I decided to chase down the source of this meme. After all, without knowing what data it is based on, it's hard to evaluate the claim's truthfulness. Below I give a description of my trek through internet history. The average-life-of-fiat meme has become particularly popular among cryptocurrency types. For instance, here is Jimmy Song, a popular bitcoin educator/developer, confidently invoking the slogan back in 2017: "When a society lacks prudence, what happens is that the society collapses or goes into chaos. It’s not a coincidence that the average lifespan of a fiat currency is only 27 years." A lo...