Everybody lies. It's a basic truth of the human condition that everybody lies. The only variable is about what exactly.
The truth begins in lies. I've found that when you want to know the truth about someone that someone is probably the last person you should ask.
You want to know how two chemicals interact, do you ask them? No, they're going to lie through their lying little chemical teeth. Throw them in a beaker and apply heat.
So that begs the question, why do they lie?