What is mental illness?!

mentally different.
they're mind is wired differently (or chemically different) from the 'norm'

When it comes to mental illness, biological/medical factors can contribute, but environmental and other factors play a role as well. Mental illnesses stem from many sources-- components that factor into a final product.

Thoughts correspond with processes in the brain, so changing the thoughts (as attempted through therapy) can change the processes just as changing the processes (as attempted with medication) can change the thoughts. Outside influences, like social support or good weather, can also make a difference.

Thinking about mental illness in this way is called the Biopsychosocial approach; is this what you were referring to in your question?

Personal Experience,
Psychology B.A. (in progress)

I think the world is to blame. It's not easy for people to deal with (life).