Unlike adults, young children think that many weird and unlikely events are impossible. Existing theories have argued that this developmental shift is driven primarily by age-related changes in knowledge as well as an increasing ability to reflect on one's modal intuitions. However, this intuition + reflection model fails to explain "when" and "why" children and adults engage in reflection. In this article, we review research on the development of modal intuitions, and we present a framework for thinking about development that connects intuition and reflection by positing that "confidence" in one's intuitions plays a key role in explaining age-related and individual differences in children's judgments of possibility.