I look at it this way.....
When one is a small baby, their world is their crib. They know of nothing else but the crib. It is the boundary of their world.
As the baby grows to a child, their world is their yard. They know of nothing else but their yard. It is the boundary of their world.
The child becomes a teenager. Now their world is their town. They know know of nothing else but their town. It is the boundary of their world.
Sadly, that is where many people stop. They never expand their boundaries after that, never expand their thinking or their lives. They live until they die in ignorance of the universe all around them.