There are ideas that are almost like formalized greetings. Everyone agrees with them, but we keep repeating them anyway, all day long. Everyone keeps saying, for example, "Human motivation is very complex." But if you stop and think about it, you have to admit that human motivation is not complex, or it's complex only in the same sense that the motivation of a fly is complex. In other words, if you try to swat a fly, it moves out of the way. And humans are the same. They step aside when they sense something coming, about to hit them in the face. Of course you do see the occasional exception—the person who just stands there and waits for the blow.
The first time I read this section, I misread "the motivation of a fly" as "the motion of a fly," so that the full sentence read, "But if you stop and think about it, you have to admit that human motivation is not complex, or it's complex only in the same sense that the motion of a fly is complex." It may be arrogant to say, but I am not entirely sure that my misreading doesn't access something deeper that is already present in the passage and, incidentally, in the work as a whole. To compare human motivation to that of a fly is a simple act of diminishment, a rough denial of the possibility of convolution in a human thought or emotion. Comparing it to a fly's motion, a repetitive and instinctual act which is nevertheless loaded with intricacy and even delicacy, smears the idea of complexity into something much richer than and less directly oppositional to the original received idea. Human motivation is complex in limited ways—its mechanics can be analyzed and even reproduced, its physics plotted and graphed, its biology transparent to the well-trained eye. But there is that intricacy, that delicacy which can be an irreducible source of wonder or disgust, an ineradicable part of our experience of the fly which eludes analysis or explanation.