In many situations, increasing task difficulty decreases thoughts that are unrelated to the task (i.e., mind-wandering). In the context of reading, however, recent research demonstrated that increasing passage reading difficulty actually increases mind-wandering rates (e.g., Feng et al. in Psychon Bull Rev 20:586–592, 2013). The primary goal of this research was to elucidate the mechanism that drives this positive relation. Across Experiments 1–3, we found evidence that the effect of Flesch–Kincaid reading difficulty on mind-wandering is partially driven by hard passages having longer sections of text (i.e., more words per screen) than easy passages when passages are presented one sentence at a time. In Experiment 4, we controlled for reading difficulty, and found that section length was positively associated with mind-wandering rates. We conclude by proposing that individuals may tend to disengage their attention from passages with relatively long sections of text because they appear to be more demanding than passages with shorter sections (even though objective task demands are equivalent).