Kevin Drum wants us to think about "aspects of human nature that most people don't pay enough attention to" and suggests a couple. I'll play! But only in a rather obvious way: I'll add the fundamental attribution error, which is more or less a cognitive bias in favor of attributing actions (of others) to their personality traits. rather than to the conditions surrounding them.
It's probably a good part of why people keep wanting to find the roots of Barack Obama's current difficulties in his personality rather than just accepting that presidents aren't very popular when the economy is in the dumps. That said, I've been re-watching I, Claudius recently, and it's just a lot more fun for Livia to be flat-out evil than it is to just accept that anyone in her situation would have murdered off and otherwise disposed of all those people.
(It occurs to me that perhaps not everyone has watched I, Claudius. It's absolutely, no question about it, must-see -- great, great TV. Plus it's short, so it's not like I'm telling you that you have to watch all seven seasons of Buffy. Which, you know, you should do to, but I'll let someone else tell you that. But really, Brian Blessed's Augustus is one of my handful of all-time favorite TV characters...highest recommendation, especially the first half of the series that he's in).