A good software is a software that is invisible for the user. This is possible by making context explicit in the software. The increasingly interest for the notion of context appears through the number of approaches based on it. Initially, context was mainly considered in engineering and cognitive science. Now even in engineering, one sees two sub-approaches considering context at the level of the knowledge or the data, namely context-based and context-aware systems. For context-based systems, most of the non formal approaches focus, in one way or another, on context in relationships with the user, aiming at a good computer system that is invisible for the user. Context-aware systems are concerned indirectly with users through a modeling of their dynamic environment. In this paper, we present, first, different viewpoints on context related to human-machine interaction. We then consider why we need to focus on users through two aspects, on the one hand, on planning and plan execution, and, on the other hand, procedures and practice. The lesson learned is that an improvement of user's support needs a consideration of context.