Teams are not machines they are organisms. To get to the full potential of a group, the group members need to have a strong bond one to each other as much as possible and the group should have as many as properties that the group has but an individual not (emergent properties). When the group reaches this potential, the sum is greater than the parts. To get there, you need to understand that a different person will have a different contribution. Never measure the individuals and compare them. measure just the group as a whole.