I have not formally studied neurology. But, from exposure to mainstream media, from what I have read, and from living in venues of mental health treatment, I have picked up a smattering of information.
When someone has schizophrenia or bipolar, the frontal lobes are affected. The frontal lobes of the human brain are thought to be the seat of human judgment, planning, and putting things into perspective.
A head trauma can also affect the frontal lobes of the brain, or it could have any of a number of effects on a person's functioning. Oddly, it seems as though some people with head trauma or perhaps a brain tumor do better in life than do some mentally ill people. Either way, you're trying to use faulty equipment while attempting to navigate in your life.
There have been numerous news reports concerning the long term effects on the brain of the repeated impacts that take place in professional football. Dementia-like symptoms have been reported. For people who have had repeated jolts to the head, I believe research is being done to find a treatment that will help. You are probably better off having schizophrenia or bipolar compared to collision induced problems, because for schizophrenia and bipolar there are known treatments that often help.
For someone subject to psychosis or some other neurological problems, sound reasoning is hard to attain and is a very valuable thing.
Without being able to reason properly and apply this reasoning to life decisions, a person lacks navigation and quickly ends up in a disastrous scenario, or has other people repeatedly rescuing them. This is probably one reason why the mental health treatment system exerts a lot of control on persons with mental illness. Some of us have not developed or have lost the ability to make sound decisions about life.
I somehow came to my senses a while back, and I believe this was due to taking a lot of time in a process of self education--teaching myself how to better use my mind. I sat in a corner of my apartment every day, played a radio, and took notes of my thoughts for several hours. I did this for several months following my most recent psychotic episode (which happened to me about eighteen years ago). And I developed my own "software" that allowed me to process information better while on medication.
Journaling is invaluable for someone who wants better use of their mind. Additionally, because I cooperate most of the time with treatment, I have steadily gained ground in respect to accurate thought processes.
If I were to go off medication and experience another complete relapse, this progress would be largely erased, and, upon reinstatement of treatment, would need to be redeveloped from square one.
I have studied my mind and have learned that the mind tends to follow the instructions that you give it. However, the very instructions that the mind follows are also the conclusions that the mind has previously arrived upon. Thus, the human mind often recycles its content. To maintain realistic thoughts, it is often necessary to incorporate some ideas other than your own.