Abstract: Most individuals consider their friends to be more positive than themselves, exhibiting a sentiment paradox. Psychological research attributes this paradox to human cognition bias. With the goal to understand this phenomenon, we study sentiment paradoxes in social networks. Our work shows that social connections (friends, followees, or followers) of users are indeed generally (not illusively) more positive than the users themselves. Five existing sentiment paradoxes are identified at different network levels ranging from triads to large-scale communities. Empirical and theoretical evidence are provided to verify the observed and expected existence of such sentiment paradoxes. By investigating the relationships between the sentiment paradox and other well-developed network paradoxes, i.e., friendship paradox and activity paradox, we found that user sentiments are positively correlated to their number of social connections while hardly to their social activity. Finally, we demonstrate how the validated sentiment paradoxes can be used in turn to predict user sentiments.