I just visited someone in a mentally ill facility recently, and it only reaffirms what I read a therapist say about it: that mental health is complete dedication to reality.
The mentally ill believe or cling on to ideas that are unreal. Those that are committed to institutations may believe that someone may hate them, or another person is jealous about their skills, or that they are the king of world, Napoleon Bonaparte, Jesus Christ. They may believe someone loves them when they don't. They may have some grandiose dreams like creating a theme park, etc.
But the more I think about it, then perhaps all of us are in some ways mentally ill. It's just that those in mental wards believe in it too much and impose it on others to the detriment of society. For the rest of us, with our mentally ill ideas we keep secret.
And that's why we all need therapy. For those of us who are not committed (yet), we harbour our own grandiose ideas, ambitions, longings, desires, fears, paranoia. The desire to be rich, to be well liked. These goals are not wrong in themselves, and we should do our best to be creative, to excel, to change ourselves, to create in the world and in ourselves something that did not exist before.
But if reality provides feedback, then we should reconsider it with due wisdom and diligence, we should take both the "good" and "bad" as feedback and readjust our goals and effort accordingly instead of accusing the world.