Depression and anxiety are cruel ironies in how they propagate as illnesses. They invariantly begin as a result of something, at least. However, as those many somethings build upon themselves, like a bacterium becoming bacteria becoming a plague, the symptoms come to manifest as the result of nothing except of the time-tested commonality of their presence, comparable to a vampire invited into the home returning for blood whenever it chooses to take the fancy. Even where there is a trigger, it is hardly ever something the neurotypical mind would glance twice toward in retrospection - a tendency, may I add, that is far too often so scarce of the neurotypical mind. These afflictions act as a magnifying glass to darkness, and a fog before light.
Oh, then, what horrible plagues befall those with the great misfortune to have been blessed with the accursed traits of benignity, for what comes of that beautiful, innocent naïveté is, by definition, unwarranted. This is the macabre irony of the human condition.