There's a genetic component to depression, there is a societal component to depression, and there are situational components to depression. A lot of therapy is

There's a genetic component to depression, there is a societal component to depression, and there are situational components to depression. A lot of therapy is to identify rumination when it happens so that you can short circuit that neural pathway (thought process) and focus on being more realistic (ironically) or in the moment. You can think of depression as a deep neural network that's been overtrained on certain inputs to always predict depression. A life or death scenario forces you to act in the moment and decide in the moment (or very near future). That short circuits the rumination as well. Maybe it is an entirely different brain system as well.