Explanation
The distinction that decides whether one works is question versus topic. An explainer aimed at a topic has to be comprehensive and will lose; an explainer aimed at a single question that sounds wrong until it is answered has a mechanism, which is surprise followed by resolution.
The other requirement is an ending that tells the viewer what to do with the information. People save things they intend to use, not things they found interesting, and an explainer with no consequence attached gets watched and forgotten.
The common mistake
Optimising an explainer for watch time. It is good at saves and sends, which most ranking systems value more highly, and stretching one to hold attention longer usually costs the save it would otherwise have earned.