What sort of things?

Don’t you hear some of the Stoics or Epicureans or Platonists say that, while some of them know all the doctrines, others do not, although in other respects they are quite reliable?

True enough.

Then do you not think it a very laborious business to separate and differentiate those who know from those who do not know but say they know?

Very.

Then if you are going to know the best Stoic you must go and make trial of most of them if not all, and take the best as your teacher, first training yourself and acquiring the power of criticism in such matters, to prevent your preferring inadvertently an inferior one. Just think how much time it needs! I left this out on purpose not to annoy you, and yet in matters of this sort I think it is the one most important requirement in such matters—I mean where there is uncertainty and doubt. And this is the only sure and firm hope you have for truth and its discovery. There is no hope whatsoever apart from the ability to judge and separate the false from the true, and like assayers of silver to distinguish the sound and genuine metal from the counterfeit. Were you to come to your examination of the doctrines with some such power and skill, all would be well; if not, you can be sure that nothing will save you from being dragged by the nose by them all or from following a leafy branch in front of you as sheep do; you will be like water spilt on a table, running whithersoever someone pulls you by the tip of his finger, or indeed like a reed growing on a river bank, bending to every breath of wind, however slight the breeze that blows and shakes it.