Moral questions are sometimes complicated. Unfortunately, choices are at times not strictly black and white. Social lies are acceptable in the context of not hurting a person's feelings regarding minor issues, such as a question about someone's style of dress or appearance. More complicated issues sometimes come down to the lesser of evils.
Although not true in every case, lying can be acceptable when it eases suffering. When an old man on his death bed or in a nursing home mistakes someone for his long-dead beloved wife, it is more ethical to go along with it to ease his last moments on earth, for example, than to correct him and add to his misery.
Lying is largely considered long. There are times, however, when it is appropriate to lie. When telling the truth could cause harm or extreme hurt then lying is not only okay but tactful. The gray area in lying is that those who do it often tend to learn how to use it selfishly to manipulate situations in their favor.
Lying may be acceptable in situations where revealing the truth may cause more harm than good. For example, revealing the truth about an affair could destroy a couple's marriage. Pretending to know nothing in this instance may at least temporarily keep the couple's marriage intact. In another situation, if someone knows about a slanderous remark about a friend, it might be better to not tell the friend about the remark to avoid hurting his or her feelings.