NUM384 Like an advertiser of any product who is worried that his or her product be perceived properly and not seen in a bad light, Judaism is careful that its product, that is, Judaism itself, is understood properly and not seen in a bad light.  Therefore, when a Jewish action is correct but the perception is negative, Judaism says the action should not be done, even though it is not wrong.  The classic example of this is the concept of marit ayin, in which a Jew may not do anything that is perceived as improper even though it is perfectly permissible (Shabbat 146b). Thus, an observant Jew should not enter a nonkosher restaurant merely to make a phone call because it may be perceived by others that this observant Jew is eating in this nonkosher establishment.  This very idea saved the entire Jewish people from destruction.  After the Jews made the Golden Calf, God wanted to destroy the Jewish people for their sin.  In order to save them, Moses argued that if the Jews were to be destroyed, the Egyptians would say that God destroyed the Jews because He was too weak to bring them in to the Promised Land, not because they had sinned.  Even though God was certainly strong enough and the Egyptian argument was factually false, God still did not destroy the Jews to avoid this possible misconception.  In a similar sense, a Jew must act in a manner that will be perceived as proper not only in the eyes of God but also in the eyes of his or her fellow Jew. The entire concepts of Kiddush Hashem and Chillul Hashem, sanctifying and desecrating God's name, are based on this idea of how people will perceive God.  If God’s perception is diminished because of a Jew’s actions, it is a sin.  If the perception of God is enhanced because of a Jew’s actions, it is a big mitzvah [Maimonides, Hilchot Yesodei Hatorah 5:1-2]