Rule of law
It is revolting to have no better reason for a rule of law than that so it was laid down in the time of Henry IV. It is still more revolting if the grounds upon which it was laid down have vanished long since and the rule simply persists through blind imitation of the past.
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From an article by Jill Lepore. I still do not understand how she's able to produce so much (deeply researched) content.