Institutio Oratoria

But the thing itself has an extraordinarily powerful effect in oratory. For the nature of the speech that we have composed within our minds is not so important as the manner in which we produce it, since the emotion of each member of our audience will depend on the impression made upon his hearing. Consequently, no proof, at least if it be one devised by the orator himself, will ever be so secure as not to lose its force

For when we have done all this, we may still account ourselves only too fortunate if we have succeeded in communicating the fire of our passion to the judge: consequently, we can have no hope of moving him if we speak with languor and indifference, nor of preventing him from yielding to the narcotic influence of our own yawns.