The point is, understanding and predicting behavior and thoughts are what the science of psychology does. We human beings are indeed intuitive scientists of our own, the difference is that we don't rely on systematic methods, like scientists do. We have our own personal constructs, which we use to try to predict future events. These are a kind of personal theories. That doesn't mean these are totally subjective like art, because the best personal constructs, are those that make the best and most accurate predictions, the personal constructs that best allows us to understand and predict events.
Understanding and making statements about reality, is not comparable to making statements about the value of art. Truth is not subjective, value judgments are.