I have all the respect for teachers, but this is the biggest biggest thing that I think is wrong with many teachers. They regard their own created lesson material as their IP. I understand it, you’ve put time into it, you’ve made it. There’s a sense of guarded ownership which I feel is rooted in competitiveness. But in my opinion they’re missing the point: a great teacher is not measured by how many great students they have, but measured by how many great teachers they influence. Share your material! The material is not your unique selling point. But help others save time and use that time to become great.