I believe it is probably referring to another quote: "The road to evil is paved with good intentions." Of course, that is just going off the words. Perhaps the timing of how each word is said could make a difference? You say you made that quote? It's interesting that the human mind can think of something with a highly philosophic meaning, without knowing what that meaning is.
I think it means that, if you say it like this, "The sin arrives within; true to itself." It means that even the worst sinner still knows he has sinned, and probably has a tiny bit of a craving for redemption.
If phrased like this "The Sin arrives; within true to itself" it means that even if you don;t know you've sinned, you still have.
These are both just possible explanations, and it could mean something entirely different to other people, it is just my observation. Also, apologies for missing any other phrasings, I could only find those two to make sense.