Tell Me Where is Depression Bred, in the Heart or in the Head?

I was lurking around the Twitterverse a little while back and wasting time, as is my want when work is slow and dull, when I saw a post of epically dumb proportions. Dumb tweets are nothing special: there are probably more of those than there are dust mites in our beds. However, l felt compelled to respond to this one in particular because it was a statement I had heard at several points in the past.