The Dunning-Kruger effect is a fascinating one to me. The short version is that people who are incompetent at something vastly overestimate their skill and ability at it and also have no idea how very terrible they are at it (and extremely competent underestimate their abilities).
To me, every aspect of it is endlessly interesting to me. The more I learned about it, the more entranced I became. I recommend that you just do some research on it, even if it's just reading the Wikipedia page I linked to.
So what does it mean for writers? As a writer, our goal should always be improvement. I know the Dunning-Kruger effect is alive and well because all of my writer friends shudder when they look upon the work they made in high school or earlier. Same old story: I thought it was the best thing ever, and now all I can see is how awful it is in every aspect.
But how come my friends can recognize it now? It's because they continued to improve. They stopped being incompetent at writing, which allowed them to recognize their former flaws (also part of the effect). I think that the best approach is to seek knowledge more than skill. The more you know about writing, the more you can see whether or not you are making use of that knowledge. Other than that, if people who you trust can suggest methods for improvement (as opposed to simply criticizing it), that can be the gradual nudge needed to start the growth.