The ICT sector has seen many improvements in productivity and efficiency in the past decades. However, its total energy consumed, as well as its carbon emissions, has never decreased. This is mostly due to a systemic phenomenon called the rebound effect: although each process consumes less energy, the global increase in process usage results in an unexpected growth in carbon emissions. In this paper, we present energy-efficient techniques and we argue why it is necessary to combine efficiency with a new approach. This novel approach is digital sufficiency, involving users and developers to reduce the demand in addition to efficiency improvements.