For some people it could be as simple as realizing that your brain is screwing you over, and therefore you can't merely intellectualize your way out of depression. Your grey matter is (mostly) fine, but it's swimming in a soup of self-perpetuating depression chemicals.

It's all but impossible to force yourself to be happy when your brain is chemically forcing you to be depressed.

It would be awesome if a magic pill existed, but for now the most effective way to reboot your brain chemistry might just be exercise. I joined my local gym, and made myself go regularly by promising myself that I'd only ever listen to my favourite podcasts while in that building.

I now consider myself fully cured.