system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do mental illnesses such as schizophrenia and depression occur in humans? Are they considered mutations or are they genetically wired in our brains that will emerge when a significant event occurs?
gpt
You can also ask how we think. 


We know we can be happy or sad depending on recent events. for some those feeling can stretch for days. Almost anything which happens a little in all of us happens a lot in some of us.

There is a genetic component to many mental illnesses. That has been established by studies. There are also signs that mental illness develops at certain stages of life.

Most are not due to new mutations. 

Exact cause and effect cannot be determined.

Those who have studied it can only tell us some of the traits and who is more susceptible. They cannot predict mental illness.