How reliable are MicroSD cards?

MicroSD cards seem to be the preferred storage for Raspberry Pis and many other SBCs. Of course, there's other applications for microSD cards -- cameras, smart phones, gaming consoles...and other stuff I'm sure. But sooner or later, people start to run into issues with their microSD cards, which begs a question -- just how reliable are they? When I first started searching around for an answer, I got a range of different answers -- some people said "modern flash should last practically forever"; others said "they should last for at least a million program/erase cycles"; while more pessimistic sources said "don't expect them to last more than a few thousand program/erase cycles". But empirical data seems to be hard to come by. So...about a year and 10 months ago, I set out to answer this question. (Well, truth be told, I was actually trying to answer a slightly different question -- but it quickly morphed into this one.) And since then, I've acquired 256 microSD cards of various brands ... Read full article.