Dopamine gets released, or not. Receptors pick it up, or not. Serotonin, same deal. We get depressed, we get happy, if we're lucky we muddle along at content, and we think it's all our outlook or our circumstances, but we don't know. Diet and exercise and medication and psychoanalysis and in the end, it's all up to what synapse fires when and whether or not the rest of your brain is looking when it does.
To all of my friends with depression or anxiety, just know that it's not your fault, that no one with a brain thinks it's your fault. And to all of my cheerful friends, the optimists and the seers of the silver lining, realize that you didn't just "choose happy", that you have chemical and reactive help in your head that not everyone else has.
And to all of my friends who have lost someone to the serotonin and dopamine imbalances, know that they were strong, not weak. To be strong every single moment of your life except for one, to only let your guard down and succumb once in an entire lifetime, is beyond my understanding. I admire their tenacity during the struggle and don't fault them their moment of weakness. But it's hard sometimes.