This. To this day I don't fully understand this behavior. Why commit a major offense for something insignificant? Ok, you ran a half-marathon, great. But if I learn that you didn't, it's going to be super weird, and probably damaging forever.
On the other hand, I do understand this behavior. When you first meet a person, those "insignificant" details actually give you a lot of information. You connect a few dots and get a straight line going upwards. That's why narcissists tend to keep you at a distance - they don't want you to see more of their "dots."
Also, there's good evidence that narcissism is just a bad case of instant grafitication. Small daily lies fit into that framework perfectly.