Okay kiddo, have you ever played connect the dots? The closed graph theorem is kind of like connect the dots but with math.
Imagine you have two dots on a piece of paper and you draw a line between them. That's just a simple connection. When you play connect the dots you try to make a picture by connecting different dots together.
Now imagine you have a bunch of dots on a piece of paper and you start connecting them together. If you connect them in a certain way, you might end up with a picture that you can see. But if you connect them in a different way, it might not look like anything at all.
The closed graph theorem is like a rule that says if you connect the dots in a certain way you can always make a picture, or in math terms, you can get a certain result. But if you connect them in a different way, you might not get anything at all.
This rule is really helpful for mathematicians because it helps them prove things. They can use the closed graph theorem to show that certain things are true, and they can use it to figure out how to connect different ideas together.
So, in summary, the closed graph theorem is like connect the dots with math. It helps mathematicians prove things and connect different ideas together.