There are countless scholarly studies from the fields of cognitive psychology and social psychology on almost every mental tool in this book. I’ve restricted myself here to the most important quotations, technical references, reading recommendations and observations. Most of the quotations I’ve left in their original language. I see myself primarily as a translator of these scientific studies into everyday language. My goal is to make philosophical ideas and scholarly insights applicable in daily life. I have the greatest respect for the researchers who study these intellectual tools scientifically.