Could the man who says "I am a liar" be wrong, rather than lying?

1st person is immature or unpredictable as he is not fully truthful.LYING is a sin in general.BUT to s ave someone.to avoid conflicts or for a greater cause lying or avoiding to reveal the .truth is imperative.If I lie unnecesarily I can not expect truthfulness from him.Sometimes good persons may also lie out of fear.Only saints and sages are said fully truthful.To achieve that fit is GOD gifted.We,He the ordinary human beings are not fully truthful.Hence we can not expect it from others.But we may try to avoid telling lies off and on and avoid such persons.