Rebuke that Will be Heard

The author of the Glilei Zahav explains the importance of proper rebuke. “A person with the ability to protest his friend’s wrongdoings and fails to do so is considered to have done these sins himself, as our sages tell us in Shabbos. This halachah is alluded to in the verse, 'אם לוא יגיד ונשא עונו'—‘If one fails to tell, he will bear his sin.’ Although literally this verse discusses one who refuses to testify on behalf of his friend, we can also explain this in terms of rebuke: Failing to give rebuke to another makes one responsible. One is considered to have done the sin if he had the power to prevent it but couldn’t be bothered to take the sinner to task.
He added, “In this vein we can also explain the extra vav in the word לוא, which indicates ‘to him.’ This teaches that one is only held responsible if he failed to give rebuke to a person who may be moved to change his ways. Regarding one who is certain to ignore rebuke our sages say that there is a mitzvah not say what he knows will not be accepted.”
Those who learned at Yeshivas Lomza when Rav Eliyahu Dushnitzer, zt”l, was mashgiach, were astounded by the sensitive manner in which he gave the students rebuke. He was always good-natured and, with a sweet smile on his face, would gently explain where the student had erred.
“He wouldn’t leave before saying to the young man, “Please forgive me.”
Naturally this would surprise the bochur. After all, why should the Mashgiach apologize?
But the bochur was not left to puzzle this over for long. “Surely you wonder why I ask your pardon. Our sages tell us that just as it is a mitzvah to offer rebuke where it will be heard, it is also a mitzvah to refrain from saying what will not be accepted. I therefore apologize if, chas v’shalom, you are in the second category. Not only did I fail to fulfill the mitzvah, I also caused you unnecessary pain. For this, I apologize.”