Teenagers seem to know everything, because they do not want to be taught through lecturing via their parents stellar reasoning skills. They respond positively and with little argument, when they know they are safe and when they know their parents “see” them and want the best for them. This originates from a parent who knows themselves, and can through their own actions (not words) signal to their kids that they have integrity to their beliefs. You cannot tell kids (or adults) what you are to them, you are to them what you are to them, not what you want to be to them.
How many kids and adults alike respond with a, “I know”, when we try to enlighten them with our stunning wisdom? People say they “know” when a reason that is proffered lacks potency, has been over explained or does not make sense to them. Until we have developed very high levels of cognitive, emotional and perceptual maturity, and are open and honest with ourselves and others, we will always choose emotionally and then find proof externally to justify our emotional decisions.