In any project, you can distinguish certain types of knowledge
Knowledge that practically does not change over time.
Algorithms, computer science, the mechanisms of the YAP and its API, etc.
Knowledge about the set of technical solutions used in the project.
Programming languages, frameworks, libraries, etc.
Knowledge that is applicable exclusively within the framework of the current project.
They are not transferred to the outside world in any way and, having left this project, you can forget about this knowledge.
Naturally, this also works in the opposite direction — to add a new person to the current project, you need to train him a certain minimum amount of this project knowledge - without which a new participant will not be able to perform useful work