Intuitions, attitudes, images, mind-wandering, dreams, and religious messages are just a few of the many kinds of uncontrolled thoughts that intrude on consciousness spontaneously without a clear reason. Logic suggests that people might thus interpret spontaneous thoughts as meaningless and be uninfluenced by them. By contrast, our survey of this literature indicates that the lack of an obvious external source or motive leads people to attribute considerable meaning and importance to spontaneous thoughts. Spontaneous thoughts are perceived to provide meaningful insight into the self, others, and the world. As a result of these metacognitive appraisals, spontaneous thoughts substantially affect the beliefs, attitudes, decisions, and behavior of the thinker. We present illustrative examples of the metacognitive appraisals by which people attribute meaning to spontaneous secular and religious thoughts, and the influence of these thoughts on judgment and decision-making, attitude formation and change, dream interpretation, and prayer discernment.