The biggest SEO misconception that I can think of on a practical basis is that people just need to "target the keywords the right way."
The problem with this is you're focusing on keywords.
This will be an issue because people search in Google in different ways for answers to a question they have.
And keywords are just one manifestation of this.
You have to dig deeper in the search process to get your content in front of the right eyeballs.
When you're stuck on keywords, you then go down the rabbit hole of keyword density and all that stuff, and you may end up settling for, maybe, 30% of the otherwise 100% results you could've been getting.
So is there a better way? You bet there is a better way.
Study the keywords you're targeting.
What is the search intent behind them? What kind of experience are people looking for when they find content that meets their search intent?
If you start thinking along these lines, the quality of your content starts to change, and the journey that people go through to find your content also starts to change.
This may be the gamechanger you're looking for if you want to earn more money with your online publishing efforts.