But a main lesson you could be taking is that you shouldn't trust your own self assessment. If you think you're good at something, don't take your own word for it.
Another main lesson you could be taking is that this paper is flawed and doesn't actually prove anything about self-assessments in general, so don't automatically second-guess anyone's word for it, even your own. Find the link elsewhere in this thread titled "what the Dunning-Kruger effect is and isn’t".