Robert M. Sapolsky said this quote

If I had to define a major depression in a single sentence, I would describe it as a genetic/neurochemical disorder requiring a strong environmental trigger whose characteristic manifestation is an inability to appreciate sunsets.

~ Robert M. Sapolsky

On 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. Sapolsky

Depression is not generalized pessimism, but pessimism specific to the effects of one's own skilled action.

~ Robert M. Sapolsky

Prior to the monotheistic Yahweh, the gods made sense, in that they had familiar, if supra-human appetites—they didn’t just want a lamb shank, they wanted the best lamb shank, wanted to seduce all the wood nymphs, and so on. But the early Jews invented a god with none of those desires, who was so utterly unfathomable, unknowable, as to be pants-wettingly terrifying. So even if His actions are mysterious, when He intervenes you at least get the stress-reducing advantages of attribution—it may not be clear what the deity is up to, but you at least know who is responsible for the locust swarm or the winning lottery ticket. There is Purpose lurking, as an antidote to the existential void.

~ Robert M. Sapolsky