Despite the many negative aspects of life in cities, urban promises of economic prosperity, freedom and happiness have fuelled the imagination of generations of migrants, who have flocked to cities in search of a better life, invariably exaggerating the opportunities and neglected the potential disadvantages of their choice. This paper uses insights from psychological literature to better understand why people have such strong, positive and apparently overrated expectations about cities. We dwell into concepts of bounded rationality to describe the cognitive biases and heuristics affecting decision-making under uncertainty and apply them to the way individuals perceive and act upon the promises of urban life. By linking this literature to urban theory, we can better understand how individuals make their decisions about moving to and living in cities. We thereby offer an understanding of urbanisation and migration processes departing from economic rationality assumptions and explain the remarkable attractive force of cities throughout human history. Finally, we discuss the ways in which human biases in favour of city narratives and bright urban futures can be exploited by 'triumphalist' accounts of cities in policy and media, which neglect the embedded injustices and structural problems of urban life.