If you live in a baboon troop in the Serengeti, you only have to work three hours a day for your calories, and predators don't mess with you much. What that means is you've got nine hours of free time every day to devote to generating psychological stress toward other animals in your troop. So the baboon is a wonderful model for living well enough and long enough to pay the price for all the social-stressor nonsense that they create for each other. They're just like us: They're not getting done in by predators and famines, they're getting done in by each other.
Robert M. SapolskyOn an incredibly simplistic level, you can think of depression as occurring when your cortex thinks an abstract thought and manages to convince the rest of the brain that this is as real as a physical stressor.
Robert M. SapolskyBut often, it's easier to resist temptation with distraction, or to be so inculcated in doing the right thing that it's automatic, outside the frontal cortex's portfolio - Then it isn't the harder thing, it's the only thing you can do.
Robert M. Sapolsky