Rationalist accounts of the development of folk-psychology maintain that the acquisition of this capacity is aided by special-purpose mechanisms rich in innate structure. Rationalists have typically maintained that false-belief understanding (FBU) emerges very early on, before the age of two. To explain why young children nonetheless fail the false-belief task, rationalists have suggested that they may have troubles expressing their FBU. Here I do two things. First, I argue that extant proposals about what might prevent children from expressing their FBU (...) cannot explain some of the relevant data. Second, I put forward a new rationalist proposal, the processing-time account, according to which young children fail because they cannot carry out all the required processing in the time available. I argue that the processing-time account overcomes the challenges extant rationalist accounts face while being compatible with the evidence in their support, thereby providing a compelling explanation of the development of FBU. (shrink)