I'm incredibly optimistic and am content with my position in life. My default state is being mindful of the present and I don't think about things too far into the future. I very rarely ever feel stressed out over things in life.
However, none of that changes the fact that I feel completely empty and find no joy in things. Interests are nearly non-existent, emotions dialed to 1, and the only thing I'm motivated to do is lay in bed staring at the ceiling... unless I'm on sertraline.
Admittedly that's just anecdotal, but I worked in a clinical neuroscience lab researching treatments for severe treatment-resistant depression (read: people who tried so many options including CBT that they even tried electroshock therapy). The only thing that helped those subjects was a regimen of personalized neuroimaging-guided transcranial magnetic stimulation for 10 minutes every hour for 10 hours every day for a week. Even then, it wasn't permanent. Some saw improvement for months, others only weeks.
For some people, it's not just a matter of "perspective".