Or, perhaps, the role of faith in life. Not faith in Something Higher Than Oneself, but rather faith in one's self. The idea runs something like this: I "know" that X is true, and (double) checking that X actually is true is boring/painful/etc., so I don't check. (Here X should be taken to be a statement about another person's behavior.) The line here between a healthy self-esteem and arrogance, closed-mindedness, condescension, and all the rest is not clear to me. In fact it's not clear that there even is a line; it could all be arrogance, closed-mindedness, and condescension.
This is a bit of a shame, as I do this all the time. Past performance may not be indicative of future results, but I'm such a creature of routine that I automatically assume the same of everyone else. And just because I've been right 347 of the past 349 times doesn't mean that I'll be right this time.
For example, this can make student interaction troubling and time-consuming, as students often ask questions with "false" suppositions. Technically, when a student with a 35 average asks if they can pass the class if they get an A on everything that's left in the term, the answer is "Yes" (depending on your grading scheme, of course). However, the compulsion is strong to answer "Yes, but if you had the ability or drive to get an A in the rest of the class, you wouldn't have a 35 now." I'm usually not that blunt, but I do make the point that you will need an A on everything else, no margin of error, and do you really know what it takes to get an A on a quiz, let alone the final? (Side story: in my current class, I have 175 homework questions assigned throughout, all officially due at the end of the term. I have several students who don't understand why I'm getting on their case about their poor homework record; they have a whole weekend left to do it all. There's only one who didn't even try to start until this weekend; the rest had at least done a set of 15 or so.) And I know if I asked four different higher-ups the appropriate tone to take, I'd get seven different answers. (Five different ones in person, with a couple of carefully-worded e-mails.)
And of course, the same is true in personal relationships as well. (The post is tagged "whiny narcissism" for a reason, people.) I remember arguing with my therapist back in college about whether it was a good idea to cruise bars looking for women. My points back then (and they're my points now too, 'cause I'm that stubborn) were (1) bars are both boring and sickening (that much cigarette smoke gives me large headaches) and (2) "she likes bars and I don't" is not the greatest basis for a relationship that I've seen. Her point was (3) you've got to do something, dammit. The problem is that I "know" what the results are going to be (with a record like mine, who wouldn't?), and I don't like headaches, so why even go out when you can do interesting Google searches?
I need a crisis of faith.