What are system, user, and assistant roles? Definition and business implications

A call to a modern LLM is not a simple text query, but a list of messages, each labelled by its role. Three standard roles exist: system (a permanent behaviour instruction, invisible to the end user), user (the message sent by the user), and assistant (the model's previous responses, kept to allow conversation continuation). The system role is the most powerful and least used lever. It sets tone, format, ethical constraints, permanent context elements, and forbidden behaviours. Well written, it avoids repeating these instructions in every user message. Misused, it is ignored or contradicted by later user prompts. The assistant role often remains invisible but plays a key role for agents and multi-turn chatbots: it lets the model retain the context of previous exchanges without having to repeat them on every call.