To make a big difference for a lot of people, it helps to start by targeting the smallest possible group you can change.
As you grow, you can jump to a bigger pond, creating more impact in the process.
Repeat as needed.
[It is a common misconception that goldfish can’t grow bigger than their tank. While that it is sorta true, goldfish—like most fish—are indeterminate growers. In other words, they never really stop growing. When properly cared for, there’s no telling how big they can get.]