Depression is a very difficult disease to treat. Patients may not immediately present with “I feel depressed.”
They might come in saying my appetite has changed. I don't have the energy for things that I used to, or it's left undiagnosed, and the patient simply suffers at home with it without presenting at all because there is a stigma in coming forward with, say, mood symptoms, and sometimes there is a diagnostic challenge in that.
There isn't a one-size-fits-all approach to treating depression. While there are many different drugs to treat depression, they don't have extremely high effectiveness in everybody. So, because of the high burden of illness, we are left with a lot of people who really need new treatment options.