We all tell lies, it is part of human nature. Sometimes we need to protect ourselves, and that is a good thing. I’ve always told my children that the truth will get them into less trouble, and sometimes, as long as I stick to my word, they do confess. But lying to your therapist is like cheating on a diet or plagiarizing a university essay and getting a high distinction. It is self-defeating behaviour and the only person who loses out is you. But why do we do it? What purpose does it fulfil?