Why is a piece of content locked?

Lock due to the principle of sequentiality:
Modules and episodes follow a sequential order, which means that you need to complete the previous content in order to access the next one. Make sure you have completed all previous content before trying to unlock the current one.

Content not yet released:
The content may not be available because it has not yet been released. The releases of the modules occur gradually over time, following a precise schedule agreed upon with the client company.