1 The most interesting part is the fact we are starting to lie when we are starting to speak. I think it's interesting from the psychological point of view.
2. I think people usually lie about small trivial things, that don't really matter to anyone. But of course there are other causes.
3. Lying can make feel better, they don't need to worry about the truth. Some people just lie for fun and they just feel better when they do it.
4. I don't think all lies are equally wrong. There's a difference between lying what you had for breakfast and for example cheating on your partner.
I agree with the 4. answer