Some theories are not confirmed by empirical research. The Case Study One case report of a child who was abused who grew up to become an advocate for children suggests that people strive to overcome their childhood problems. But one case report doesn't show us how typical this outcome is. If the sample size is large enough, the population is represented accurately. The preceding descriptive studies just looked at overall averages.
Correlation allows prediction.
We search for general principles that apply both in the artificial but controlled laboratory and in the realistic but uncontrolled everyday environment. Of course, but there is an underlying similarity among people, too. They are less complex than humans. These include a chapter overview, self-tests, and other resources.