To me that shows why we CAN NOT use the scientific method in our personal relations. Suppose I have a friend at work who's usually polite and helpful. Then one day I notice that she's being rude, ignoring her duties, and so forth. If I insist on judging the situation based only on observation and logical deduction, I would have to conclude that she's somehow turned into a bad person. However, I also have another option: I can have faith in this person. And that's a perfectly reasonable thing to do. Her change in behavior may be resulting from something I don't know about, such as an illness, a family crisis, or something else. It may be something that I never know about. Nobody can ever observe another person thoroughly enough to completely understand all of that person's motivations, emotions, reasons, and thoughts. Hence, forming judgments about people solely by observation and logical deduction cannot truly be enough.
Again, slightly paraphrased. He's right. Human beings are too complex to be treated to a facile application of the scientific method.