The ancient theory of thirds says that in any organization, team, business or industry association, one-third of the people will do two-thirds of the work. The next third will do the remaining work and the last third will do almost nothing. If you belong to a group of any kind, think about the members and you will see that this is a pretty fair statement, and has been for thousands of years.
The theory can be extrapolated to mean that the first third of the people in an organization are the leaders, the second third are the followers, and the last third barely contribute. It is almost impossible to motivate this last third to become an active part of the group. That’s not to say they don’t want to be a part of the organization, or that they lack interest. Sometimes, we just need to be a passive part of a company.
The people who make up those thirds ebb and flow; for a year or two (or many) one person will be in the first group and then slide to the next group and perhaps to the bottom to rest for a while before coming back to the top again. Somewhat like the globes in a Galileo thermometer, we drift up and down, as our time and energy and interests permit. It does not make us less a part of things, simply less involved.
Make sure those people in the resting phases of membership continue to feel valued, acknowledged and welcomed; eventually they will lift themselves up into the activity once again. Ask for their help, their opinions and their contributions, but don’t press. Remember that most people are members of multiple and varied organizations, and unless you’re Superman or Wonder Woman you have probably resided at the bottom third of at least one organization at any given time. Silent support is still support. Make sure your organization is one of inclusion, no matter what third people find themselves in.