On the most successful teams in any field, the individuals who constitute high achieving teams will often share common skills, but with a key difference among them: focus. Where their focus lies is what helps them specialize and excel in their role, and drives success for their team.
Take sports teams, for example. In a hockey team, all must be exceptional skaters, have excellent puck handling skills, and be able to pass the puck accurately. But some specialize in goalkeeping, some in defense, others in offense. For the team to succeed, it needs its individual components to be laser focused on their role.
This is not unlike a project team.