Many contemporary scholars have recently defended the idea that the agency of things is symmetrical and equivalent to human agency. We propose an alternative approach to artefacts’ agency based on a field study concerned with contextually situated observations of the process of design of artefacts in Amazonia. By means of participant observation and interviews, we address the role of artefacts in relation to human agency. In so doing, we focus on the human-unique capacity for design as it is related to cognitive resources such as intentionality, decision-making, planning, and volitional adaptations of the material world to human purposes. We argue that such cognitive resources are ultimate manifestations of human agency. The findings allow us to conclude that artefacts possess a special form of agency, which operates in different ways from the agency of true agents. This agency is derived: it depends on the actions of true agents, with either function as remote intentions or are required for the artefact to work at the moment of use. Thus, the relation between artefacts and agents is asymmetrical. Given that the derived agency of artefacts allows people to expand their own agency, we propose the notion of enhanced agency for the prosthetic incorporation of artefacts into the agentive capabilities of human agents.