Many people will tell you that depression is caused by a chemical imbalance in the brain.  It is not.  It starts with your thinking, gets followed up by your energy, gets exacerbated by the circumstances that appear in your life (because of your thinking), and then your brain starts to change.  It gets a new ‘set point’.  It’s like “what came first the chicken or the egg”? What came first the thoughts, the depression or the changes in the brain chemistry?