Mine was genetics. My dad had schizophrenia and some people on his side of the family also had it. I don’t know about any stressors. I worked in a hospital for years and it was always stressful.
I think it is usually a combination of genetics with environmental factors. Nothing else explains , for example, the increased risk factor of identical twins but it not being assured that they will both develop sz. IMO there has to be a genetic component mixed with other factors to explain most cases.
I’m interested in figuring out what events cause each specific diagnosis, but I thought a general ‘mental illness’ poll would be a good starting point.