I can tell you, after 27 years as trial lawyer, that every human being lies. Not always, but often enough that you should maintain a healthy skepticism. I questioned literally hundreds of witnesses in deposition or at trial, and I can tell that, without fail, every single one of them lied to me at least once. They lied about important things and unimportant things, they lied for understandable reasons (to avoid getting fired or losing money or going to jail) and for inexplicable reasons. They lied even when it was obvious to the most casual observer that they were lying. I never took it personally. Instead, I just pinned them to their lies and then used other evidence to discredit them. And even today, when I am retired, I take what people tell me with a grain of salt.