Fact checking is something we'd often prefer not to do. Even the best critical thinkers can be deluded, mistaken, or swayed, when it suits us.
When you have something contentious to say to another person there's a good chance that they won't hear much after the first line. This means they'll miss the point of what you need to say, and the subtlety of your argument. Your eloquence will be wasted.
We can all fall into the trap of creating a self-fulfilling prophecy by anticipating, say, failure or difficulty. A more subtle but equally effective strategy for limiting our outcomes is to make hasty judgements, either because we don't think about it or because we go with someone else's opinion without checking for ourselves. I originally wrote this for some notes on my Difficult People training, but it applies to many situations where we label things.