@cnavarro495649 Not sure if you still need this but I'm just gonna say it here because the link provided is broken. Basically the issue is the difference between REQUIRED and SUFFICIENT. "The door is the only way in and out of the house" is required because the argument is done for if we negate it. But once we add "locked door is impenetrable" it becomes sufficient because it's too much, since the argument simply does not require that second part to be true along with the first part (only the first part is enough). If it's by itself it would be a required and less important assumption.

If you check the second example about the caffeine, the book included "very tempting, but more than we need" to the assumption that is quite similar to this one.