Positive emotions are prevalent on Social Networking Sites (SNS) because of positive shift—users’ tendency to shift the expression of their emotions in the more positive direction. Emotion expressers aim to gain a more positive impression and elevate their social standing through positive shift, but little is known about the unintended consequences of positive shift for the expressors. Drawing on social projection theory and emotional journey theory, we argue that positive shift can lead to social projection and reduce the expressor’s perceived honesty of other SNS users—an important antecedent of trust and satisfaction with SNS, and this is more likely to occur when the user shifts emotions with higher emotional dissonance (i.e., difference between expressed and experienced emotions). We further propose a diversity reminder as a likely remedy that suppresses the social projection process. Using two experiments, we found evidence supporting these predictions. Our findings provide important implications.