Epistle XCIV — On the Value of Advice
Just as the the student of javelin-throwing keeps aiming at a fixed target and thus trains the hand to give direction to the missile, and when, by instruction and practice, he has gained the desired ability, he can then employ it against any target he wishes (having learned to strike not at any random object, but precisely the object at which he has aimed), — so he who has equipped himself for the whole of life does not need to be advised concerning each separate item, because he is now trained to meet his problem as a whole; for he knows not merely how he should live with his wife or his son, but how he should live aright. In this knowledge there is also included the proper way of living with wife and children.
Seneca Epistles 93-124, Translation by Richard Gummere. Loeb Classical Library.