Our brain controls everything we do and think and what happens in our body. Who directs these complicated brains? “I” do? No, there is no central power or police force, no editor, prime minister or CEO, no leader. The brain controls all without a director.
What causes your depression: serotonin or what you experience? The answer: the question is invalid! Both play a role, and are interconnected. You cannot say that one of these is the cause.