Natural selection has produced not only fixed adaptive traits in response to enduring environments, but also contingencies capable of yielding variable outcomes in variable environments. A well-known example is phenotypic plasticity, which entails alternative developmental outcomes in different environments. Here, we focus on more immediate and transitory behavioral plasticity (underpinned by motivational processes), and we suggest that the physiological concept of homeostasis offers a coherent perspective for studying human motivations and associated behavioral processes. We further propose the asymmetric behavioral homeostasis hypothesis, which conceptualizes many motivational processes as 1-sided homeostatic mechanisms and which predicts that motivational responses that are amplified by certain cues will not be reversed simply by reversing the input cues. An important implication is that many evolutionarily adaptive-albeit subjectively and socially deleterious-responses to fitness threats (e.g., fears, aversions) are more easily inflamed than dampened. We review literature bearing on this hypothesis and discuss implications for psychology.