Some [...] virtual agents are entirely automated, others are a “human-in-the-loop” system, where algorithms take “machine-like” subtasks and a human adds creativity or execution. (In some, the human is training the bot while she or he works) The user interacts with the system by either typing in natural language or speaking, and the agent responds in kind.

I'm most interested in the highlighted part. I think that the interaction is where the success of AI is decided - when it feels natural.