As teachers, we're so used to giving away our knowledge for free. About 10 years ago, I wrote some lesson content for an online educational company, trying to supplement my income with a side gig. My contract paid $50/lesson. I soon realized that it took me the better part of a Saturday or Sunday to write each lesson to the company's standards, do all the wiki formatting, include an assessment for each lesson, and input any required edits. So, I only wrote about 7 or 8 lessons for them before deciding it wasn't a good use of my time.
Recently, I visited the site to grab some published writing samples of my work to use for another job application. I was shocked to see that some of the lessons I wrote have been monetized hundreds of thousands of times! Now I'm even saltier that they only paid me $50/lesson! It was a good reminder to remember my worth, and not give away my expertise (practically) for free.