Purpose: Human life is connoted by sophisticated interactions that involve not only single individuals, but larger social groups composed by members interacting each other. Cooperation secures a benefit to all the people engaged as well as important behaviors like helping, sharing, and acting prosocially. But what happens when the joint actions are not effective? Materials and method: In the present study, we asked 24 participants paired in 12 dyads to cooperate during an attentional task in a way to synchronize their responses and obtain better outcomes. In addition we tested inter-brain and cognitive strategy similarities between subjects. Then, we frustrated their strategies by providing false feedbacks signalling the incapacity to create a synergy, which was reinforced by a general negative evaluation halfway through the task. The effects of the feedback inmodulating subjects behavioural performance and brain responsiveness were explored by means of functional near-infrared spectroscopy (fNIRS). Results: Results showed a worsen performance after the negative feedback in the form of longer reaction times and a specifc pattern of brain activation involving th dorsolateral prefrontal cortex (DLPFC) and the superior frontal gyrus. The DLPFC showed increased O2Hb (oxy-haemoglobin) level after the feedback, compatible with the need for higher cognitive effort. In addition, fNIRS measures revealed a decreased inter-brain synchronicity in post-feedback condition for the dyad. Also, the representation of negative emotions in response to failing interactions was signalled by a right-lateralized effect. Conclusions: Results were interpreted at light of available knowledge on perceived self-efficacy and the implementation of common goals and strategies.