True enough. And then, we need to ask, how many are needed to convince The Decider to make the decision you want made? That will vary, of course. Most Deciders have constituents. If most constituents are already convinced and The Decider is ignoring or even repressing them, you start thinking about regime change. In any event, your number is not just about opinion, which is only the first step; you need to get a number to commit to action and to success.
At that point, if you are working with any size organization or populace, you must think about coalition, since, as Saul Alinsky reminded us, those who are committed already to an organization will, if their organization commits to your cause, also be committed and your cause becomes their cause.
A coalition that will win needs a goal that not only is appealing to many groups but is not alienating to huge numbers. This may mean attempting to gather together some of the leadership from various stakeholder groups to see about formulating such a goal. What are the considerations for that group?
Part of goal formulation is to determine the end goal, which should probably be more specific and realistically doable than 'Happiness for everyone on Earth', but more ambitious than 'Reserve a room for us all to meet.' I generally think in terms of establishing a long-term meta-goal (350 ppm CO2) and a three-six month goal (agree on a fossil fuel divestment resolution and get 50 groups to pass it, all the way from activist organizations to college Board of Trustees to local units of government to small businesses).
Goal formation with all participating stakeholder groups is a consensus process. No group will participate with any meaningful effort if they are outvoted at this stage. So you, as the one committed to formulating a coalitional goal, need to find out, either in private caucus or in a group process (which could even be done online in some innovative ways), what are desires of the various stakeholders and what are dealbreakers. Dealbreakers, of course, may be what cannot be a part of the goal or what must be a part of the goal. Discussions can only fruitfully move toward the goal formation if the potential field of goal description avoids all dealbreakers. If that proves impossible, it may be that your coalition is untenable and one or more members need to drop out. Usually, however, if the meta-goal is agreeable to all, defining the near-term goal is doable. Assign a high-medium-low importance to the desires, or wants, of each stakeholder group, and you can seek a negotiated near-term goal with likely success, says Larry Dressler (2006, p. 63).
One of the toughest ways to get to a consensed-upon goal is to start from announced positional goals of the stakeholders--but it happens. At that point, you will need to haul out all your techniques toward a good principled negotiation process and final result, with a final result ready to put into play almost immediately.
Then, when you achieve your short-term goal, you can use that victory to tune-up your next goal while you use the victory to encourage more individuals and the general public to feel like it's time to join your movement because your movement has shown that it is a winner.
Movements in the past have learned lessons, but there are always new areas of exploration into how to achieve something. Occupy was such an exploration, with two commitments that I argue were mutually exclusive, radical inclusivity (Maharawal, 2013) and consensus. If everyone is invited to help decide, and if everyone has the power to block decisions, the only decisions possible are those that will be more or less ineffective in the end. Occupy was not a top-down phenomenon, so no rulings on process nor decisions were vetted by anyone at a Mother Ship or party headquarters. Still, consensus had to be modified to make many of the simplest decisions or any crank, street psychotic, Tea Party belligerent, or law enforcement/corporate infiltrator could easily derail everything.
Dressler, Larry (2006). Consensus through conversation: How to achieve high-commitment decisions. San Francisco, CA: Berrett-Koehler.
Maharawal, M. (2013). Occupy Wall Street and a Radical Politics of Inclusion.Sociological Quarterly, 54(2), 177-181. doi:10.1111/tsq.12021