One concept that people often miss when structuring groups, organizations, or social spaces is the importance of those who aren't here. People who aren't actively present can be just as important for the medium- and long-term future of your project as those who happen to be around right now (sometimes more so!) -- and if you overfit your planning to the people who happen to be around right now, you may end up damaging your long-term prospects.
Here are some examples of what this can look like:
1) A king falls into decadence and surrounds himself with flattering courtiers. Whenever he wonders whether things are going in the right direction, the courtiers assure him everything is grand and maneuver to prevent him from learning about any negative developments.
2) An online community is meant to represent a wide range of viewpoints and perspectives, but biases in moderation begin to creep in that drive some away. Since the people who don't agree with the current approach have mostly left, polling active users no longer accurately samples the broader community that the space was meant to draw on, but rather the people who happen to agree with the current approach.
3) An employer begins to remove people who don't agree with his strategy and hire those who do. Now, everyone in the organization is on the same page with respect to the strategy -- but when that strategy has flaws there are few internal voices that are able to point that out.
4) A person who recently moved is having some social difficulties fitting in to a new community she's joined and asks her old friends for advice; because they are already her friends and enjoy her current manner, their advice is not very useful for helping her adapt to a new context!
5) A company developing new technology overfixates on their current market and falls prey to Galápagos syndrome; their products become overspecialized with features for their existing group and are no longer competitive in the broader market.
Focusing too much on those who are currently present can be insidious because it can be self-reinforcing; once one is focused on an inappropriately small group of users, confidants, or advisers, it can grow increasingly difficult to bring in information from outside this perspective. Further, one who relies too heavily on a certain perspective can ultimately alter their plans in a direction that further reinforces that small group's desires, driving more of those who don't agree out, and so on.
In order to avoid this cycle, it's important to "look to the river but think of the sea"; in other words, consider not just those that are currently in front of you but also the broader group you hope to reach in the longer term. Solicit outside perspectives or alternate takes and seriously engage with them when making your own plans. In some cases, doing this can be hard -- but that doesn't mean it isn't important.
After all, if you want to make a difference for more than just those you're currently interacting with, it's important to make sure you don't forget yourself in the current milieu!