No one said it was easy. But, sometimes - if you're not too depressed - if you manage enough of these enough of the time (possibly with the help of a good friend nagging you) you can get enough of a feedback loop going to self-sustain and maintain a healthy living pattern long enough to sink in.

Sometimes sure. I agree, these healthy habits are prerequisites when you find yourself more depressed than usual.

But sometimes these healthy habits aren't going to be enough.

Not all depression is severe depression. Same with anxiety. In many cases people can manage it by themselves (e.g. without medication or extensive counseling).