It says one of the causes is above average intelligence. That's what you get when you constantly think about things...
I don't always focus on the negative though. That's an pretty offensive comment of you. I'm going to need evidence from your side to even barely trust that.
The positive makes me happy, and I've taken all the positive moments in my past and used them to maximum to hold my ground. I've been drowning in so much positive stuff I'm fearing that something must be negative, something is lurking and awaiting to strike. That has always happened when I got happy again, every time.