My whole life my family asked, "Why do you make a funny face in all family photographs?" My honest answer is that I think that lining people in a row and telling them to smile seems like a recipe for crazy. "Okay, line up. Pretend you're happy." Even if I was happy before, I'm angry now, because now I have to portray my happiness for future reference.
Now when I take a family photo, I show my true happiness. I think about my gratitude that people related to me invited me into their home and gave me free food and didn't ask me for a loan. I feel gratitude that someone wants to record and remember being in my company, and I smile out of pure joy.
My family hates this.
Now they show me photos and ask, "How come in family photographs you always look like you're stoned?" My honest answer is that until I graduated college, being intoxicated was most of my emotional experiences of acceptance and joy. It's my primary reference for how to smile.