What field of science could be more solid than geology? Rocks are visible, tangible. You can bang on them with a hammer, drill them, compress them, zap them with X-rays, ultraviolet light and radar, analyze their chemistry, extract their secrets.
The study of human behavior, by contrast, is the story of science’s struggle to identify the ineffable. Researchers have taken wildly different approaches to trying to figure out how people think and behave, from Sigmund Freud’s notion of the Oedipus complex to making behavioral science more “scientific” through efforts such as the Diagnostic and Statistical Manual of Mental Disorders and fMRI brain scans.