Damn. This is gold. Truth right here. This hit me right in the gut when I read it.

I'll probably never get my mythical trauma memoir written, let alone published, but if I do, I'd like to include this idea and cite you with your permission.

"You can't choose to be happy. You can only choose to act happy."

I'll add that it's especially easy to act happy when you're terrified because very bad things have happened to you when you've admitted you're depressed.