It is not possible in this context to give more than “some guidelines” in this complex matter. We will also modify the question slightly.
Classic tochacha is done to change the mind of one who sinned knowingly. Although the mitzva exists nowadays, most authorities assume that it can be accomplished satisfactorily only by those people who are uniquely qualified or those with a special relationship to the recipient.[1] We will therefore concentrate on the related mitzva of afrushei me’issura (keeping a counterpart from sinning) by informing someone who does not know that he is sinning. The S’dei Chemed[2] maintains that afrushei me’issura is derived from the pasuk of tochacha, although others contend that it is only a Rabbinic obligation.[3]
The first guideline is mutav sheyihiyu shog’gin v’al yiheyu mezidin – when one is sinning unknowingly but will continue to sin knowingly if he is informed, it is better that he should not be told.[4] This, however, applies only when one is sure that the person will not change his ways.[5] It does not appear that one needs 100% surety, and it is very difficult to decide when to use this distinction. One of the cases in which pointing out a particular mistake is less likely to be successful is when many people act improperly in this matter.[6]
The possibility of a negative backlash is also a factor. In a landmark teshuva,[7] Rav S.Z. Auerbach argues that one may even participate in a situation in which he knows that a person will be doing something wrong – ostensibly violating lifnei iver[8] – if drawing attention to it would cause that person to deteriorate further and incite hatred of the Torah and its adherents. Certainly then, one can refrain from interjecting when this is likely to cause significantly negative results in addition to probably not helping. We use some variation of this concept often in our interactions with the non-observant and those with inconsistent observance, although, in all honesty, it is not always clear when our silence is due to prudence and when it is to avoid uncomfortable conversations.
It is important to consider that it is not always a choice between whether or not someone’s mistake should be corrected, but when, how, and by whom it should be done. Consider the following historical facts.[9] Yaakov, Moshe, Yehoshua, and Shmuel all waited until close to their deaths to strongly rebuke their constituencies, out of concern that a rebuke at an earlier time might cause the recipients to change their allegiances in favor of a path of evil. Similarly, a rabbi in a new position may see many things that he knows his community needs to change. Instead of raising all issues at once and failing, he likely should wait for a (hopefully) opportune time to deal with each (or some) of them.
An interesting question is whether one should get involved when he sees someone who is unaware of the issue doing something that is forbidden according to a majority of opinions, but regarding which there is no unanimity. Again, we will borrow a concept from Rav Auerbach’s approach to lifnei iver. According to most poskim, one who is stringent on a certain questionable practice may enable one who is legitimately lenient on the practice to partake in it.[10] He does not have to apply his own standards regarding a possible violation on someone else. Rav Auerbach[11] goes a step further. Suppose that Reuven, who is doing the questionable thing, is unaware of the majority view forbidding the matter and the legitimate minority who are lenient. Even then, Shimon may enable Reuven to act if he knows that were Reuven aware of the various opinions, he would act leniently.