I would like to give you one explanation that comes from my field of activity. It has to do with the design of human-computer-interaction or better: human-automation-interaction. Very often tasks are too complicated to be fully automated. At certain points of the solution process the user has to be incorporated.
Researchers found that a "mixed initiative interaction" is most suitable for this type of tasks. In mixed initiative interaction the system acts an an "agent", that is as an equal partner to discuss with during the solution process. This strategy aims to support and encourage the human decision making and problem solving skills.
With the concept of mixed initiative interaction in mind, the human-like communication style in user interfaces can be explained. It is often the most intuitive way to simulate the artificial agent working on a task together with the user. Below you find an article on this topic. It contains an example (the software "Lookout"), where human and computer negotiate about appointments. The user states his preferences, the computer checks the calender and confirms or makes alternative suggestions. The communication style of human agents is used, for example the artificial agent says: "You will be busy at that date, should I suggest another date?" This contributes to a natural flow of information exchange between two agents that aims to find a solution that is acceptable for both parties.
Summarizing, you can simulate a personality if human computer collaboration is essential for accomplishing a task and if a human-like dialog supports the human decision making process. Depending on the particular application there can be different ways to design mixed initiative interaction.
The cash machine example can be related to mixed initiative design as follows:
- At the point where the message appears the successful completion of the task not only depends on the machine, but also on the user, because the transaction cannot be completed if the user interrupts the machine or if he goes away.
- Therefore the user has to be prompted to wait and in order to make this comprehensible a reason has to be given ("the server has to be contacted").
- The I-perspective further increases the trust in the system and the confidence in a successful completion: It leads to the mental model "Ok, there is an agent doing its best to provide the desired service to me, I do what he asks from me". It also reduces the technical nature of the message. If the message was for example "Please wait, the system has to contact the server", the technical nature of the message could intimidate the user, he could even take it for a problem.
Reference: Hearst, M. A. (1999), 'Trends & Controversies: Mixed-initiative interaction.', IEEE Intelligent Systems 14 (5) , 14-23 .