In other words, psychotherapy cannot spawn the regrowth of brain tissue formally occupying the enlarged ventricles within the brain. Clearly, there are biological differences here between the healthy versus the pathological brain. These changes cannot be not reversed, despite a successful resolution of psychological issues, had there been any before the onset of illness. Nor do these changes seem to be reversed upon treatment with antipsychotics or other somatic treatments. Once induced, schizophrenia often remains recurrent or chronic, despite psychosocial influences.
Schizophrenia is thus biological de facto.
Hard work does not make it less so. I chose schizophrenia as an example because the biological pathology is so easily recognized. Another striking example of a mental illness that's biological phenomenology is easily recognizable is bipolar disorder. The cycle evidenced by the dramatic switches between severe depression and mania can be so regular as to allow for the prediction of mood states hours, days, weeks, or months in advance. There are people who follow a 48 hour cycle regularly for extended periods of time.