In 2018 we inhabit a “post-truth” world where scientific evidence and accurate information must compete with appeals to emotion and “fake news”. In this talk I will attempt to shed some light on the human tendency to believe “alternative facts”. For one thing, individuals tend to restrict the amount of information they collect when forming beliefs, “jumping to conclusions” on limited evidence. In an era where dubious claims are routinely propagated by highly visible individuals, it is little wonder that mistaken beliefs – “misbeliefs” – about empirical reality persist in the face of contrary scientific evidence. Alongside a generalised tendency to jump to conclusions when forming beliefs, however, is a pronounced failure to form beliefs dispassionately. Instead, humans are disposed to form “motivated” beliefs. In particular, we are prone to a desirability bias, being more inclined to accept evidence if it supports what we want to believe. Finally, some beliefs may be held for social rather than epistemic reasons – that is, to signal commitment to cultural groups upon which individuals depend.