Answer:
Sanity is just having the same mindset as others, Society determines whether a person is sane or insane.
Explanation:
Sane: Free of mental illness and in a reasonable state of mind, mentally healthy.
Insane: mentally deranged, insane actions. They can have Paranoia, Distrust of humanity, they can be Vengeful, etc...
How to know if you are insane or turning insane: Sleep or appetite changes, Mood changes, Social withdrawal and loss of interest in activities previously enjoyed.