Underthinking was a technique used by inhabitants of the Edgeworld to prevent waifs from hearing their true thoughts. To underthink, an individual would conceal their true thoughts with false thoughts. Waifs learned to underthink from birth, and most people thought that only waifs were capable of underthinking, but some individuals from other species were capable of underthinking as well. Underthinking was near-universal among waifs in the city of Riverrise under the rule of the Riverrise Custodians, for anyone detected harbouring negative thoughts about the custodians was killed.