LEV539 We are sometimes obligated to relate derogatory information. Rabbi Chayim of Volozhin said that the Torah wrote the two prohibitions together to teach us a lesson. When it is necessary to relate derogatory information to save someone from harm we must do so. Withholding such information is a violation of the prohibition against standing idly by the blood of your fellow man (See Chofetz Chayim, R'chilus 9b:6; The Ohr Hachayim and Malbim also discuss this idea.). Rabbi Simcha Zissel Ziv comments that from here we see how much effort it takes to do exactly what is proper. Since speaking loshon hara is an extremely great transgression, a person might be inclined to avoid it by resolving, "I'll always remain silent and I won't talk at all." But this is not permissible. There are times when one is actually obligated--not merely allowed--to relate derogatory information. (Chochmah Umussar, vol. 1, p. 332). Some people are normally careless in regard to speaking loshon hora. Yet they avoid relating information of practical importance, such as information in connection with a shidduch or a business partnership. In such matters, failure to relate the necessary information could cause serious harm and damage. For this reason, it is of the utmost importance to know the laws of loshon hora very well. A person must know when he is obligated to be silent and conversely, when he is obligated to divulge information. (Zeh Hashulchan, notes of sefer Chofetz Chayim).