"De theorie is goed."

Vertaling: The theory is good.

[PietHijma]

The theory is right. What is wrong about that?

[swift-tutle]

If a theory is RIGHT, it means it's true. It means it's proven and is now the real explanation for the observations your theory is about. If a theory is GOOD, it means it is likely to be true, the best explanation for the observations to this day and matches with the current understanding of the world.