I often hear people say stuff like "I just know. I feel it in my gut."
I have come to the conclusion that this is code for something like "I have no idea, but I really want this to be true."
Sometimes the feeling is in another organ not traditionally associated with thought, like the heart, or the liver. Or sometimes, it's the mysterious "I feel it in my waters," wherever the hell they are.
Hearing this is an indication that the speaker is not in the possession of any facts.
I find myself unimpressed by how strongly someone can believe something with no evidence. Stronger belief ("I really feel it to be true") in the absence of evidence is, if anything, an indication of stronger willingness to fool yourself. That's hardly compelling. I am not sure we should be convinced by how deeply gullible someone is willing to admit to being.
I recommend thinking with the organ that is best fitted to the task. Use your brain. Give it some data. Examine the evidence and think about it. With your brain. You might even find out something about a little thing I like to call "reality".
The "gut feeling"/"I just know" shtick tends to come at the end of an argument (generally an argument the "I just know"-person started, what's more), right about the point they realize that everything that they initially stated as if it were unquestionably true has been shown to be wrong, or at best irrelevant to whatever they were trying to argue for.
It comes at this point because it's the ultimate safe argument, since you can hardly argue with "feelings", but it's also the ultimate contentless argument - it's an admission that they have no actual grounds for their position at all. How do we know? Because if they did, then we'd be discussing the grounds, not their mysterious "feelings".
On Certainty: People that claim to be certain are nonetheless frequently wrong - it happens all the time. Indeed, I've argued before that other things being equal (like strength of evidence in favour), you're more likely to be wrong when you're certain you can't be mistaken, because it means you're no longer considering disconfirmatory evidence.
Consequently, "I know, I feel it in my gut" is a double whammy - not only is there no supporting evidence for the feeling, you're also not allowing for the possibility that disconfirming evidence even exists (otherwise, you couldn't claim to know). This is the ultimate in self delusion. It's open, in your face, deliberate self-delusion.
I find it ludicrous that anyone could say this kind of thing without expecting to be called a moron. Yet I hear it a lot. They seem to think it's somehow a clincher. In a way it is, but all it clinches is that they're willing fools.
Sure as crap rolls downhill,
it will come to pass -
if you think with your gut,
you'll talk out your ass.