People with mental illnesses and even those who are suffering from short-term depressions cannot simply “make themselves feel better.” You can’t will yourself out of mental illness. It is caused by a combination of chemical imbalance and neural pathway abnormalities in the brain.
Let me put it this way. It would be like me dropping a 50-lbs anvil on your foot and telling you that if you think positive thoughts that the broken bones will magically heal themselves. Yes, it is exactly the same. I know you don’t think so, but it really is.