If you want to teach someone a lesson, you don't start out by telling them they are stupid. I think it depends on the person. Let's consider two scenarios. 1.

If you want to teach someone a lesson, you don't start out by telling them they are stupid. I think it depends on the person. Let's consider two scenarios. 1. "Never fill in your details on suspicious sites." 2. "You recently filled in your details on xyz.com. Now I know that your credit card number is 1234." In response to (1) I would nod, but would it register deep enough? Not so sure. Now if someone actually shows me that he duped me into giving out sensitive details, I would be way more impressed and remember the lesson for longer.