Difficulty concentrating is a tricky symptom. Depressed people may have difficulty concentrating on what they want to think about, but they may ruminate obsess

Difficulty concentrating is a tricky symptom. Depressed people may have difficulty concentrating on what they want to think about, but they may ruminate obsessively on unpleasant topics. That fits nicely with the article's speculation that depression is "nature’s way of telling you that you’ve got complex social problems that the mind is intent on solving."