Research has shown that we are endowed with a remarkable capacity to motivate ourselves in the absence of extrinsic incentives (i.e. intrinsic motivation). However, little research has been conducted to investigate whether we accurately appreciate the power of intrinsic motivation. The current research aimed to examine the metacognitive accuracy of the extent to which people can motivate themselves without performance-based extrinsic incentives. Participants were presented with a relatively long and repetitive task without extrinsic incentives, and before doing the task, they were asked to predict their motivation on completion of the task. Across seven experiments using a variety of tasks with different populations from different countries, participants were consistently engaged in the task more actively than they predicted. When participants were provided with performance-based monetary rewards, however, this bias was diminished. These results indicate that we tend to underappreciate our capability to sustain our motivation without extrinsic incentives.