The worldwide yearly promotion of the World health organization's Hand hygiene day highlights the fact that guidelines are not enough to make behaviours change, even if this means to adopt very simple actions. Behavioural change in contexts characterised by high degree of complexity is the field where behavioural scientists study and analyze biases that influence sub-optimal choices, consequently implementing interventions to correct such biases. Despite an increasingly widespread diffusion of these techniques, also called nudges, there is not full agreement on the effectiveness of such interventions, whose evaluation is limited by the difficulty to ensure a full control over cultural and social processes related variables. The debate about nudges' effectiveness is important, but focusing the whole debate about Behavioural sciences implementation on specific and contextual effectiveness risks to lead to a full and detailed description of the finger, while the moon is shining elsewhere.