How can we define the term Actor? In our first attempt, we considered explaining it technically, using a threading model, concurrency, call stacks, a mailbox, and so on. Then, we realized that a technical description doesn't reflect the essence of a solution based on Actors.
In fact, every time we have to design a solution based on Actors, we can see the Actor as a human working in a company; this person has a name, and maybe an email address (Actor reference). The first important fact is that he is not alone; he is going to interact with others (messaging), receiving messages from his hierarchy and transmitting other messages to colleagues or subordinates (supervisors).
The imaginary company is structured using a hierarchy; a supervisor (user guardian) is looking at the health of its subordinate, and, when a problem is raised, if the supervisor can handle it, they will perform actions to fix it. If the error is unmanageable, the supervisor will escalate it to their own superior (supervisor...