I don't know who originally said it, but it goes like this:

"Good theories are specific enough to be falsified; bad theories are so general that they will always be true".

Is this theory falsifiable? (Or is it always "true?")
In other words: What is it that could prove this theory incorrect?

Saying that the theory is "true," and it is up to the rest of the world to prove it wrong, is backwards. It is up to the inventor of the theory to prove it.

"The confirmation of specific predictions is more informative than the confirmation of general predictions, because specific predictions have more opportunities to be disconfirmed." - Keith Stanovich, "Theories and the Falsifiability Criterion" from "How to Think Straight About Psychology" University of Toronto

(Something can seem true, especially if it overlooks facts that contradict it and embraces facts that seem to support it. So it seems "true," but "true" isn't always real.)