The previous two posters obviously haven't considered every possible option. Let's say that someone asks you where "person A" is and you expect that this someone wants to kill "person A", then it's okay and even better to lie about the whereabouts of "person A". Another possibility is to lie when you don't want to hurt someone's feelings. "I don't want to date you because you are ugly" might be honest but it also hurts a lot for the other person. Just say "I don't want to date you because I think our characters don't really match" is a lie, but at least you save someone's face and feelings.