The reason why I do that is because I've learned that "the truth" really will set you free. So if I say something that is only 50 % true or 90 % true, I will stop what I am saying out loud and I will confront myself in mid-sentence.
I learned this technique during college. And in all sincerity, it saved my life.
Do you tell yourself the truth, the whole truth, and nothing but the truth? If not, it's time to start.
The truth will truly set you free. Trust me, I know.