How are these two at all mutual exclusive?

Trying to reason your way out of mental illness is like trying to pull yourself out of quicksand by yanking on your hair. Depression screws with your thoughts and perceptions in incredibly profound ways, including your ability to make predictions about the future, and is absolutely a tamp on rational thought. That's true whether it is caused by another mental illness or a traumatic event in your life; it's just as "chemical" and just as difficult to escape either way. Throwing off depression with strength of reason or willpower is a misunderstanding of how untreated depressed people adapt and occasionally heal, not a prescription. The human body is built to survive, and the brain is no exception, but a rational person should always try to supplement their natural strength with medicine when their life is on the line. Advising anything else seems irresponsible.