What are Asagai's definitions of realists and idealists?

From the text:

What you just said about the circle. It isn’t a circle— it is simply a long line—as in geometry, you know, one that reaches into infinity. And because we cannot see the end—we also cannot see how it changes. And it is very odd but those who see the changes—who dream, who will not give up—are called idealists … and those who see only the circle we call them the “realists”!