It is necessary to be completely honest at all times in what you say and what you think if you are to return to Heavenly Father's presence in eternity and become a god yourself. Satan likes lies, and tries to convince us that there are some occasions when it is permissible to lie. He encourages us to rationalize our lies. But using any form of dishonesty is following Satan, and those who lie cannot escape punishment.
People use all kinds of reasons to try to excuse being dishonest. People lie to protect themselves or their reputations. But to God, there are no acceptable reasons for any dishonesty, whether it's an outright lie, a partial-truth, or the use of a gesture or silence to mislead someone. It often takes courage and sacrifice to be completely honest at all times.