Last November Matt Haughey of Metafilter fame wrote a great post at Medium that saw lots of pickup: Why I love Twitter and barely tolerate Facebook.

There’s no memory at Twitter: everything is fleeting. Though that concept may seem daunting to some (archivists, I feel your pain), it also means the content in my feed is an endless stream of new information, either comments on what is happening right now or thoughts about the future. One of the reasons I loved the Internet when I first discovered it in the mid-1990s was that it was a clean slate, a place that welcomed all regardless of your past as you wrote your new life story; where you’d only be judged on your words and your art and your photos going forward.

Facebook is mired in the past. My spouse resisted Facebook for many years and recently I got to watch over her shoulder as she signed up for an account. They asked her about her birth and where she grew up and what schools she attended, who her family might be. By the end of the process, she was asking me how this website figured out her entire social circles in high school and college. It was more than a little creepy, but that’s where her experience began.

I feel the same as the title of Haughey's post, and I agree with much of what he says, but my main reason for sharing his sentiment is different (or at least I think it is; Matt's a lot smarter than I am so it could be that I'm about to lay out a subset of his thesis).

Unlike Matt, I don't feel any pressure on Facebook to conform to any single consistent image of what people think I am or what I have been in the past. Many people who know me are in my Twitter follower graph also, and it's easy enough for anyone to associate my Twitter account with my real identity, so I don't think of it as a clean slate where I can be completely inconsistent with my identity elsewhere on the Internet.

I suspect many of my grade school friends who have just started tracking me again on Facebook after years of not having seen me might be surprised by my odd sense of humor, interests, and career choices, but it hasn't ever felt like a shackle. If anything I feel more pressure on Twitter to live up to the expectations of so many people I don't know who've chosen to follow me without any real-life connection.

That last point gets at what I find to be the primary difference between the two networks. To take a McLuhan-esque view of medium and message, the audience selection on each of those social networks is the primary affordance that shapes the content I create for them.

My Facebook graph is hundreds of people I've met through the years: immediate family and relatives, classmates from grade school through college, coworkers from various companies I've worked at. It's an emergent contact book more than anything else.

What it isn't, however, is an audience I can easily write for. It turns out that an assemblage of people you've met through the years is too diverse and random an assortment of people to treat as a coherent audience. What could I possibly write as a status update that would be interesting to my father, one of my coworkers from my first job out of college, the friend of a friend who met me at a pub crawl and friended me, and someone who followed me because of a blog post I wrote about technology?

This odd assortment of people all friended me on Facebook because they know me, and that doesn't feel like a natural audience for any content except random life updates, like relationship status changes, the birth of children, job changes, the occasional photo so people know what you look like now.

So unlike Haughey, what I struggle with about Facebook is not the constraint to be consistent with a single conception of myself, it's the struggle to target content to match multiple versions of myself. Judith Rich Harris' great book The Nurture Assumption was a revelation to me as it explained much of the childhood tension in my life. Harris' insight was that the influence of parents on their children's mental and emotional development paled in comparison to that of the child's peers.

More than that, though, Harris made explicit something that most of us do without ever being conscious of. That is, we play different versions of ourselves among different groups of people. Early in life, our first split in personality comes between school and home. We play one role with our parents, a different role with our classmates at school. It explains why we're often embarrassed when our friends would come over to our house and see how our parents interacted with us, because we felt it exposed a version of our personality that we tried to hide from our classmates when at school.

Later, in adult life, we have a version of ourselves that we play with our spouse or the person we're dating, another version of ourselves with our coworkers, yet another with our siblings and parents, and a different version of ourselves with our kids. Some people accumulate online peer groups, for example people they play online video games with, and that creates yet another identity.

My followers on Twitter, in contrast, are largely people I don't know. Most people who follow me on Twitter choose to do so only because they find my tweets interesting, or at least that's how I interpret a follow, especially when it's someone I've never heard of (yes, I'm aware this is reflective of some non-trivial level of self-regard, but then again I am a person who still writes a blog; I struggle all the time with the amount of self-absorption inherent in having such an online presence).

Since I interpret each new follower that way, I think of my followers as a set of people who wandered past my stage at the circus and decided to stop and watch. Each additional follower reinforces that what I was writing on Twitter before must be of some interest to them, and so it reinforces my urge to write more of the same.

Facebook, with people from all those groups as the audience, forces us to collapse all our representations into one. It's a reverse network effect as a publishing platform, where as your graph grows, the urge to publish diminishes. I see more noise in my news feed now, and it feels more and more futile for me to post anything worthy of the attention of this odd assemblage of people whose sole misfortune was meeting my corporal self.

As my Twitter follower count grows, I feel more incentive to raise my game and provide a consistent or increasing pace of high quality content. With Facebook, the more friends I add from more walks of life, the more paralyzed I feel about writing or posting anything.

Facebook does provide tools for you to solve this issue. You can divide your friends into different groups and post content to those specific subgroupings. In the opposite direction, you can filter stories of specific types and from specific people. Facebook also works hard to tune its algorithm for choosing which stories to show to whom to try to keep the signal to noise of the news feed high. And let's not forget that the Facebook graph, one that represents so many of the people I've met in real life, has its own value as it grows. It's become a valuable self-healing, self-growing address book.

But as a social interaction space, it feels like a party that's gotten too crowded. Organizing hundreds of people into groups is no fun, and I'm like most people in not even bothering (Twitter has lists, too, and I've never bothered putting my followers into any such lists). Algorithmic efforts to tune my News Feed aren't anywhere close to working judging by my recent visits. It feels like more work than it's worth to mute stories or particular people, the noise to signal ratio is so high now.

If there's one way I do feel something similar to what Haughey feels, it's in feeling more disembodied on Twitter. My existence on Twitter has always felt like it lived inside my head, in the twists and turns of my attention. My content on Twitter is ideas, links to articles of interest, mental debris. I feel more corporeal on Facebook because people post pictures of me and most of the people in my graph there have seen me in real life. Because of that, I feel uncomfortable with the fact that my avatar on Twitter now is an actual picture of myself while my avatar on Facebook is a picture of a Theo Epstein Cubs jersey. It feels reversed.

The medium shapes the message. There's a reason that the photos I post to Instagram are so different from those I post to Flickr (and it's intimately related to why it will be harder than so many people think for Flickr to co-opt the ground that Instagram has claimed). There's a reason I check-in to more places on Foursquare than I do on Facebook, why I suspect Snapchat will carry vastly different content than something like WhatsApp.

It's why, when designing a social product today, it's so important to think through the flow by which new users build their graph. Facebook's suggested user algorithm constantly finds people it thinks I know in the real world, and so that's how my graph grows. Twitter, by contrast, is constantly suggesting users who they tell me are similar to those I've just followed. Because those suggestions are likely constructed from collaborative filtering across follow patterns, and because follow actions on Twitter tend to be based on the content that those people find interesting, what my Twitter graphs have become are really finely tuned content publishing graphs, in both directions.

I agree with Hunter Walk that it will be extremely difficult for Facebook to be a supergraph that just subsumes all subgraphs by sheer size. When Hunter speculates that "each generation needs a space to call their own," I suspect that what he might be honing in on is related not to generational shifts but several natural inflection points in a person's identity. When you start going to school, your personality splinters in two, between your self with parents and your self with your classmates. For some, the shift to high school serves as another transition.

The next major transition is leaving home for college. There's a reason so many people become lifelong friends with people they meet in college but lose touch with friends from grade school or high school, because often our personalities and selves shift in huge ways until college, when we find a stable adult self.

After that, there are possible inflection points, but not ones that affect as many people. Jumping into a long-term relationship can be one (fertile cinematic ground for Judd Apatow), marriage is another for some people, and having children is yet another seismic event, though often it's less about personality than responsibility. When their kids leave the next, couples often have a moment for redefinition, which some seize. And of course, there's that moment when every woman or man morphs into that person who just doesn't give a damn anymore and just says whatever they think, becoming a sort of grumpy truthteller (think Maggie Smith's Dowager Countess in Downton Abbey or Judi Dench's M in the James Bond movies).

Hunter Walk notes that a social graph has never lasted 10 years at scale. I think there have been too many factors in play to extrapolate too much from that pattern; a lot of that was just products gone bad, or new products gone better. But chief among challenges for all graphs that are rooted in identity-related content is the difficulty of surviving the leap across these major inflection points in our personalities and selves.

One last thought on this topic: while it may be tempting to use Twitter or Facebook as an authentication system for your new website or service to try to jumpstart the growth of your product's graph, first consider if that audience is the right one for your product. They're the right audience much less often than new services and apps think.

There is no one graph to rule them all because we have so many conceptions of ourselves. The exceptions to this rule of multiple selves tend to be people with asymmetric popularity (celebrities or internet luminaries who have many many more followers than people they follow) since they tend to build up the same audience on any network they join. Rather than sharing various sides of themselves, they are just reinforcing themselves on every medium to maintain the image which brings them great wealth and/or popularity.

I used to wonder why Superman ever bothered being humble reporter Clark Kent at all. With infinite energy and the ability to fight crime effectively 24/7 on a global basis, Superman should spend all his time flying around the world checking criminals and natural disasters. Any other use of his time is criminal under-leverage of his skills.

Now that I'm older, I suspect he might just be an introvert who simply needs psychic time away from the spotlight of being Superman to maintain his sanity. On Twitter, Superman has tens of millions of followers to whom he posts photos of his heroic exploits, favorited and retweeted thousands of times, but on Facebook, as Clark Kent, he has just a few hundred friends, and he posts poorly lit photos of himself out on dinner dates with Lois Lane. Each of those photos get about ten or twelve likes each, along with frequent comments from his mother: "Cutest couple ever!!!"