If there's one insight I've had that I think is worth wide dissemination -- and I don't claim it's original, but I'm pretty sure it was independently derived -- it's this:
Our saying something does not cause it to be so. God alone can create light by saying, "Let there be light." For the rest of us, there is at best a contingent relationship between what we say and what is. Even a dictator whose word is literally law depends on those around him continuing to agree that his word is law. God alone is sovereign.
That seems obvious enough in the abstract; who would claim that their saying, "I am holding a donut," causes a donut to exist in their hand?
But if the mere fact of our saying something doesn't cause it to be so, then it follows the mere fact of our saying something doesn't mean it is so. Additional conditions are necessary.
If we know the truth, and if we intend to express the truth, and if we say something is true, then it is true.
Often, though, people rearrange this to something like: If we intend to express the truth, and if we say something is true, then we know the truth and what we say is true is true. From here, it's a short step of assuming people we like (including ourselves) always intend to express the truth to conclude that everything they say is true.
But few people are quite that simplistic. Most of us know anyone can be mistaken about some dry, external, objective fact. But who can tell you you're mistaken about some internal state or experience of your own?
So "Everything this admirable person says is true" becomes "Everything this admirable person says that refers to himself is true." If he tells you what is motives are, those are his motives. If he tells you what his influences are, those are his influences. If he tells you he has consulted his conscience to the best of his ability on the matter, he has consulted his conscience to the best of his ability on the matter. And what Catholic can criticize the actions of a person who follows their conscience?
Except: Every human can be wrong about what is true, even if -- arguably especially if -- it refers to themselves.