Human thinking and human decision making were optimized for the environmental conditions our ancestors were facing. This chapter discusses to what extent these mental adaptations are still present in everyday life and which far-reaching consequences in the context of sustainability follow from them. Adopting the theoretical perspective of cognitive psychology allows for a systematic review of typical cognitive pitfalls in decision making and dealing with complex systems. The chapter closes by emphasizing the need for explicitly considering such cognitive biases and available knowledge on them when addressing ecological problems and shows ways how this can be realized.