In principle, it is a shared vision that holds a group together, a common view of how people want things to be different in the future. If my opinion of how things should change doesn’t overlap with yours in at least a tiny way, we have no reason to work together.
It may be that we disagree on specific approaches—how much money to spend, who to hire, when to do what—but for a good group decision to result we must have a shared vision of the outcome, where we’re heading.
Practical Tip: Identify and write down what we agree that we hope to achieve. For an established group this might be a mission statement, or a vision statement, or a set of goals. For a one-time group (perhaps gathered at a public hearing, for instance), begin with a statement of why the group is gathered and make sure at the outset that everyone is there for the same purpose.
When we may be inclined to disagree, it helps to know we have the same vision.