Well, it depends on what the truth is about. If it's a personal comment on someone and is something they are unlikely to change, then it's not kind to tell the truth as you see it.
If it's something you have done wrong, then in most cases, people hide the truth because of fear of punishment. They may recognise they have "done wrong" but they don't want to have to suffer whatever punishment is prescribed. They may have been speeding while driving a car, they may well believe that it is safe for them to do so but if they are caught, they recognise that they have broken the law and are likely to be punished. They don't want that. Especially if they have previously received points on their licence and might now lose their driving licence for a while. That is a powerful incentive not to tell the truth!