We ought to give our friend pain if it will benefit him, but...

We ought to give our friend pain if it will benefit him, but not to the extent of breaking off our friendship; but just as we make use of some biting medicine that will save and preserve the life of the patient. And so the friend, like a musician, in bringing about an improvement to what is good and expedient, sometimes slackens the chords, sometimes tightens them, and is often pleasant, but always useful.