You never have "all" the facts, and in fact you have none of them absolutely (except the fact that you exist, and all of Plato's heaven which are disputably not really facts but math).  Nonetheless, you should be aware of why you believe what you believe, and you should be capable of reevaluating what you believe when new facts come to the table.  But if you can't hold that much self-reflective information about yourself, what you are likely to do instead is make up a story to fill in the gaps, and forget how the story was originally constructed with a bunch of made-up stuff.  And so you have no capability to re-evaluate the story when new facts come in because you aren't even aware of which part of the story was factual and which part was just pasted in to make a complete story.  It takes more brain power, more sugar (or ketones) to do it right, and I assert that most people don't spend that much sugar/ketones, and then it becomes very difficult to argue with them because they have such (Dunning Krueger) certainty about their pre-conceived falsehoods and no inclination to point you at how they know it... they just "know it" (but they don't). 

 I think those people just conclude that they don't need to know. I do, occasionally. Eg, someone I don't know well recently said I care about my own happiness too much. I should focus more on making others happy. She said she could sacrifice for another and I couldn't.  Ok. Do I need to argue with her about that? What will it achieve? Does she even think that or is she just saying that to hurt me or try to get me to do what she wants? Or is she right? Who knows. Some arguments cannot be won. 

 Actually no, I'm just being blinded by her pretty face. She's 100% wrong. Attacking me for being selfish, hoping that I behave how she wants me to, is 100% hypocrisy.