Coming our way via Mr. BadCatholic, Marc Barnes:
If truthfulness were merely a phenomenon of fact, then being truthful would amount to a life spent whispering “elephants are mammals” in a continuous, soothing fashion. It is more than this. It is a state of being. It describes a a quality of our existence, not just of our syllogisms. We want more than a life spent saying truthful things — we want to be truthful. Truthfulness is a virtue, an interior
disposition, a way of carrying ourselves. It is an intentional mode of being in the world, to the point that we can make sense of Kyle Morton of Typhoon when he sings “I never said I was honest. I am true.” The Catechism of the Catholic Church says it well, because it is the business of the Catholic Church to say everything well, and make you feel terrible for trying to say it otherwise:
“Truth or truthfulness is the virtue which consists in showing oneself true in deeds and truthful in words, and in guarding against duplicity, dissimulation, and hypocrisy…Truthfulness keeps to the just mean between what ought to be expressed and what ought to be kept secret.” (CCC 2469)
The mere fact of saying something true is not necessarily truthful, because truthfulness requires not telling and not showing. The Church, typical in wisdom, deepens and ennobles the entire concept. Truthfulness is a mode of being which synthesizes revelation and secrecy, balancing what is offered and what is hidden. Telling-all and revealing-much may be factually true, but truthfulness requires hiddenness. Why?
He tackles the Why question with the rest of that post. It's a good read but it will take focused attention.
So focus. And pay attention. And read the whole thing.
It'll make you understand why so many of us say, with palms facing outward and arms extended, TMI... TMI!
Carry on.