There is extensive evidence which indicates that people learn positively about themselves. We build on this finding to develop a model of team formation. We show that under complete information learning positively about oneself prevents efficient team formation. Agents becoming overconfident tend to ask for an excessive share of the group outcome. Positive learning generates divergence in workers’ beliefs and hampers efficient team formation. Interestingly, in a context of incomplete information regarding the partner’s ability, extensive learning biases may reduce the divergence in agents’ beliefs and facilitate efficient team formation as a result. We apply our model to coauthorship and organizational issues.