A simple compliment can make someone’s day, start a new friendship, or just make the world a better, kinder place. So, why don’t people give more compliments? Perhaps people misforecast the effect their compliment will have. Five studies explored this possibility. In Studies 1a and 1b, compliment givers underestimated how positively the person receiving their compliment would feel, with consequences for their likelihood of giving a compliment. Compliment givers also overestimated how bothered and uncomfortable the recipient would feel (Study 2)—and did so even in hindsight (Study 3). Compliment givers’ own anxiety and concern about their competence led to their misprediction, whereas third-party forecasters were accurate (Study 4). Finally, despite compliment givers’ anxiety at the prospect of giving compliments across our studies, they felt better after having done so (Study 4). Our studies suggest that people misestimate their compliments’ value to others, and so they refrain from engaging in this prosocial behavior.