Shakespeare calls “custom” a tyrant in Othello, when Othello says:
The tyrant custom, most grave senators,Hath made the flinty and steel couch of warMy thrice-driven bed of down.
Imagine my delight in coming across this beautiful fragment of the fifth century BC Greek poet Pindar:
Custom, the king of all / of mortals and immortals / leads, justifying that which is most violent / by its very powerful hand.
Of course the main reason why custom is so powerful is that it is difficult to separate the things that we hold by custom from those things which are in fact natural or self evident principles in our understanding.