Attamen, quae causae sunt eiusmodi, ut de earum iure dubium esse non possit, omnino in iudicium vocari non solent. num quis eo testamento, quod paterfamilias ante fecit, quam ei filius natus esset, hereditatem petit? nemo; quia constat agnascendo rumpi testamentum. ergo in hoc genere iuris iudicia nulla sunt. licet igitur impune oratori omnem hanc partem iuris incontroversi ignorare, quae pars sine dubio multo maxima est; in eo autem iure, quod ambigitur inter peritissimos, non est difficile oratori, eius partis, quamcumque defendat, auctorem aliquem invenire; a quo cum amentatas hastas acceperit, ipse eas oratoris lacertis viribusque torquebit.
(Cicero, De Or. 1.241-242)
And yet those cases which are such that the law involved in them is beyond dispute, do not as a rule come to a hearing at all. Does anyone claim an inheritance under a will made by the head of a household before the birth of a son of his? No one; since it is settled law that the will is revoked by such subsequent birth. Thus there are no judicial
decisions on this branch of the law. And so the orator may safely disregard all this region of unquestionable law, being as it certainly is by far the larger portion of the science: while, as for the law which is unsettled in the most learned circles, it is easy enough for him to find some authority in favour of whichever side he is supporting, and, having obtained a supply of thonged shafts* from him, he himself will hurl these with all the might of an orator’s arm.* These were javelins with a slinging-strap to help the thrower.
(tr. Edward William Sutton, with his note)
Crambe Repetita 