This is a short post because I do not want to lose track of what I have been observing for some time. Some of this post is based on my experience gained through recent reading and more is from observations made at home, while watching my 4 year old playing, learning & communicating; and at work, watching various colleagues and observing their styles of work.
It is amazing to see how emotional stability plays an important role in our lives. People who are more level headed (emotionally stable), have better cognitive strengths. Talking of my son, the ability seems to be changing everyday because a child’s life is easier than an adults. When he has a better day at school and has more fun at home, his language appears to be more refined and his cognition improved. On days when he has fights at schools (all boys fight at school, don’t they?. It’s possibly when he loses those..) or gets a time out, I notice his learning capacity reduced; probably because his emotions are eating out of his cognitive balance.
Possibly the same thing applies to work place. Why are some of our colleagues smarter than others, and why some of them are not as competent? The answer seems to be simpler now. Characteristics like compassion, self-awareness and self-restraint make cognitive abilities stronger, resulting into effectiveness and better productivity at workplace. Other human competencies like empathy add value to your cognitive ability. If you notice, people who are happier and level headed, perform better than stress heads. I am not sure whether vice versa is true or not.  The theory surely applies to testers too, but I am not sure if it can be correlated with ability of finding defects in a product. We might have to sponsor for a study in this field.
Just my observations. I am still learning!