This article addresses the relationship between humans and the built environment, particularly in the context of (chronic) illnesses. In environmental psychology research, this relationship is described as transactional, as humans and their environment constantly influence each other. In cases of illness and disability, dependence on the environment increases because the fit between person and environment diminishes. The fact that the environment shapes physical condition as well as cognitive and social abilities should be considered at all levels of planning: from neighborhood design to individual furnishing. People with impairments can reveal weaknesses in the built environment due to their heightened sensitivity. Planning should be less oriented toward the average population and instead critically examine the fit between people and their environment, especially for those with impairments. Only then can a truly human-centered design of the environment be achieved.