Programmers! Did you know you can fairly choose a random item from a list in a single pass, without knowing the total number of items in advance, and in constant, minimal space? This delightful method has lived rent-free in my head since I learned it from the Perl gods in the 90s: https://csg.sph.umich.edu/chen/Perl/cookbook/ch08_07.htm
The method has a name — Reservoir Sampling! (Thanks 
@shaprShae Erisson)
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