This article aims to analyze the factors influencing belief in a flat Earth. We focus on Spain, a country that sadly has some of the most relevant figures on this topic in the Spanish-speaking world. After a qualitative analysis of YouTube videos on the main channels on the subject, a survey was carried out on 1252 individuals. The results point to two conclusions. First is the presence of a considerable Dunning-Kruger effect among flat-earthers. There is a significant negative correlation between science literacy-overall and practically all its dimensions-and overconfidence in science in this group. The second, evaluated through a regression tree, confirms that the interaction of low scientific literacy and overconfidence is highly relevant in explaining the belief in a flat earth. Neither factor alone is determinant, but the combination of the two (low scientific literacy and high overconfidence) leads to high levels of flat earth belief.
Keywords: Dunning–Kruger effect; flat earth belief; overconfidence; scientific literacy.