New research, published by the Rockwool Foundation Berlin (RFBerlin), shows that co-workers can have powerful—but opposing—effects on the careers of young workers. While some colleagues foster learning and long-term success, others may hinder career progression through direct competition. The study follows young labor market entrants in Germany without formal qualifications and examines how the quality of co-workers in their first job shapes long-term outcomes. At first glance, co-worker quality appears to have little overall effect. However, this masks two offsetting forces.