Why marathon finish times spike at 3:30 and 4:00, and what that says about every threshold you've trusted (danluu.com)
Dan Luu's 2020 essay maps the spikes that appear wherever a hard threshold sits: 9.8M marathon finishes clump at round times, Polish exams bunch at the pass mark, drug charges pile up exactly at the sentencing cutoff.
The thread adds fresh cases — chess ratings, AWS gaming its own P90 latency target — and one self-correction: a commenter called the lead example bogus, realized it predated a policy change, and withdrew it. The marathon spikes turn out to be social, not just vanity: pace-runners with flags.
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