  We study how disagreement influences team performance in a dynamic game with
positive production externalities. Players can hold different views about the
productivity of the available production technologies. This disagreement
results in different technology and effort choices -- "optimistic" views induce
higher effort than "skeptical" views. Views are changed when falsified by
evidence. With a single technology available, optimists exert more effort early
on if the team also includes skeptics. With sufficiently strong externalities,
a disagreeing team produces, on average, more than any like-minded team. With
multiple technologies, disagreement over which technology works best motivates
everyone to exert more effort.
