There is truth here, but depression is also accompanied by a feeling of powerlessness, and a fatalistic belief that one's lot cannot be changed.

We all have highs and lows, and life is clearly not fair. The difference between those who are chronically depressed (barring medical conditions) and those who bounce back to a better place is the belief that one can attain a better existence. And due to this belief, corresponding actions occur to make it so.