Why Can't We Admit That Our Lives Aren't Perfect?

A post on the New York Times blog Motherlode is getting lots of buzz today. In it, the divorced mother of a young son writes very honestly about watching other family's lives around her, on Facebook and in real life, and wondering if they're as happy as they appear or if they're merely struggling to maintain a facade of perfection.
Amy Lawton writes:

Why is it so hard to have honest conversations about things that really matter? Not politics or books or current events – those things are easy to talk about. It’s our own vulnerabilities that get stuck on our tongues. Is this true just for me?

How would you answer her?
Lawton did a fantastic job of writing about this issue by being vulnerable and open in her post, admitting that she's not at all happy with her divorced status, that she envies the families around her, and that the nights without her child seem to last forever.
But the larger issue she writes about has bothered me for years. I know that my own life is far from perfect -- I struggle as a wife, as a mom, as a stepmom. I struggle with my purpose in life and my direction. I struggle mightily to find happiness. Yet people outside my home probably would think things appear to be just wonderful.
Is this true for you, too? Why do we all feel the need to constantly convince others that we're "fine?" We're "happy?" We're "okay?"
Even when we're not.
I think the uncomfortable flip side of this issue is that most people don't really want to be around a person who's down and openly admitting it. We call them whiners ... complainers ... Debbie Downers. We're shocked by the things they admit in the car rider pick-up line or on Facebook. We're judgmental. Everyone gets a pass to complain once in a while, of course, but when someone seems to be down a lot, that person is generally avoided by others. It's sad but true.
All this doesn't really make me want to run to Facebook and write about my troubles any time soon!
Those are my thoughts on the matter. What are yours? Are you a "creeper" like Lawton, watching other families who seem to be happy together and wondering if you'll ever have that kind of happiness as well? And why do you think we have such a hard time being honest with each other about our lives?