This contribution seeks to illuminate the looming phenomenon of demultilateralisation and the return of and to the nation state, i.e. closure. Whereas many reasons for opening and closure have been discussed by Habermas in his eminent essay, we aim at providing an additional dimension, taking a psychological point of view and analysing this proclivity from a behaviourally informed perspective. Following a short recapitulation of the evolution towards postnationalism, we briefly sketch the current phenomenon of demultilateralisation and renationalisation. We then contribute to the current debate by providing cognitive psychological insights drawing on well‐researched biases that offer the greatest potential to explain the current outbreak of closing tendencies, namely prospect theory, including the endowment effect, framing, the availability bias and so‐called hawkish biases. This may add an explanatory dimension to why nationalistic politics have become again the beguiling sanctuary of the people. We attempt to define scope conditions of closure.