The Sages enacted certain prohibitions out of the concern of "Lazut Sefatayim" – rumors and allegations that might spread as a result. These laws forbid one from placing himself in a situation which would result in people speaking about him negatively and spreading embarrassing rumors about him.
A classic example of this Halacha is a law codified in the Eben Ha’ezer section of the Shulhan Aruch (12) regarding a woman whose husband has gone missing, Heaven forbid. The woman in such a case is an "Aguna" (literally, "chained"), meaning, she is unable to remarry, because she has not received a Get (divorce contract) from her husband, and her husband has not been confirmed dead. Halacha allows such a woman to remarry based on the testimony of a single witness that her husband died. Although Halacha generally discounts testimony that is rendered by only one person, and requires at least two witnesses for any legal matter, the situation of an "Aguna" is an exceptional case where the testimony of even one witness is accepted. However, if one witness testifies to the husband’s death, thus permitting the woman to remarry, the witness may not marry the woman. If he would marry her, people would likely spread rumors that he in truth did not see the husband die, and gave false testimony about the husband’s death so that he could marry the wife. In order to avoid these allegations, a witness is not permitted to marry the woman who became eligible to remarry based on his testimony.
However, if two people testify to the husband’s death, then one of them is allowed to marry the widow. People are not likely to allege that somebody falsely testified so that somebody else can marry the woman he desires. Therefore, if there were two witnesses, there is no concern of rumors, since it does not seem probable that the witness who marries the woman persuaded his fellow witness to falsely testify. It is only when the testimony is given by one witness that people may accuse him of rendering false testimony if he marries the woman.
Summary: The Sages enacted several prohibitions to avoid the possibility of false rumors and allegations about a person. Thus, for example, if a witness testifies that a man died, such that his wife is able to remarry, he may not marry the woman, as people will suspect him of testifying falsely so he could marry her. If, however, two witnesses testify, then one of them may marry the woman.
