“Interaction” Design: A play of sand and waves

I believe Interaction design is, quite literally, the process of designing what kind of interactions would happen within a system, and each of its users, and between the system and each user. A simple analogy that comes to my mind right now is of a beach and the waves. A system has the character of a beach, which has its own working and meets the users at a rough line, and users have the nature of the waves, unpredictable and free-willed.