A simple way to understand the difference between OER and ZTC

The most useful knowledge I learned this week is to understand the concept of ZTC. OER and ZTC can be seen as products of different purposes. In order to better remember the difference between OER and ZTC, I made the above picture. Personally, I think this picture can be a very simple and clear way to understand the difference between OER and ZTC. Hopefully you can see the meaning of the picture:)