Pop culture is full of stories of split personalities and double identities. Think of the masked comic-book superheroes who hide their faces and names while saving the world: Peter Parker and Spiderman, Bruce Wayne and Batman. Think of a bloodied and bruised Brad Pitt in Fight Club. He was really Ed Norton, right?
Trace it back more than a century to The Strange Case of Dr Jekyll and Mr Hyde and the terrible serum that transformed man into maniac. But admit it. You're already leading a double life. So is your partner. Almost certainly your kids are too. Do you really know them at all? There's who you really are, in the flesh and face-to-face, the values you hold and what you think. Then there's the mask you wear online, how you filter what you do for broadcast on social media to friends and family, and how you behave in the digital arena.
For example, the Pew Research Center's latest Internet & American Life research paints a picture of citizens' concern that they don't own or control their data online. In the post-Snowden era, there's a growing awareness that data is being quietly gathered about our online habits by corporations and governments; sometimes with our consent and sometimes covertly. But it doesn't stop people sharing their data freely. Problem is, if you regularly use social apps and digital tools - even down to email - giving up their use is easier said than done.
One commentator has described today's digital citizens as "useful hypocrites". We say we care, but we use communication channels because of a combination of peer pressure, unwillingness to pay for alternative services and the reluctance to take practical steps like encrypting email because it feels too much like hard work. But the social web has never been about being authentic. It's about being a version of yourself that you are prepared to share. You're funnier, smarter, more attractive and fitter on social media by virtue of how you filter the stories you tell.
We self-censor on social media - 71% of us start to write posts, think better and delete. We tend to avoid controversial subjects that might annoy or alienate family and friends. Social media gives you chance to "personality hack" and present the best of yourself to the world. But there's also an all-too-human gullibility that goes with it.
We know we filter our own profiles but we still believe what we read about others. It's the challenging sentiment behind Tinder's controversial new ad campaign about sex trafficking that invites the user to think differently about the profiles they are looking at. Or it's why online scams persist, from phishing emails that persuade people to part with personal details, or even honey traps that persuade men, largely, to part with their money and common sense.
Ironically, there's now a growing digital trend that's pulling in the opposite direction. The odds are, you're telling those social tales on the same mobile device that's increasingly the repository of data about your lifestyle. Want to know the facts about your health and fitness? You used to have to ask your doctor. Want a view of your productivity? That was a conversation with your boss. Want to know if you've had a solid night's sleep? Well, that was something either your bathroom mirror or your partner told you in the morning. Now, the odds are you'll ask your phone.
There's been growing consumer interest in body hacking apps since 2009 - smartphone apps that measure and record lifestyle data and spit out trend-based recommendations about sleep patterns, diet, even how long you've been sitting peering at a computer screen without a break. There are hundreds of apps to choose from: from blood pressure recorders to tools to monitor your menstrual cycle. This is the era of data-driven optimisation of the self. Track and trend line your habits and diagnose what you may never have thought was wrong about your life and learn how to fix it. Google's search trend data suggests that come New Year - you know, that moment that everyone reflects on wanting to be a better version of themselves - there will be a spike in interest in apps that help quantify the self and optimise your lifestyle for health, fitness or productivity.
Wearable tech - from patents for earbuds that capture biometric data to Google Glass and smart watches - are well suited to measuring performance passively. You won't need to input data, the device will capture it as you go about your daily routine. But there's evidence that the hype about wearable tech is yet to translate into consumers seeing such devices as essentials for modern living - with a tendency for early adopters to abandon devices in six months.
Which brings us back to privacy concerns. Here data collection can be both active and passive; actively logging calorie intake or passively gathering data about your movements via the device's accelerometer. Who owns that data you are creating - whether actively or passively? Do you own and control it? The device manufacturer? The app producer? Will health care providers want to receive streams of such data in future?
So welcome to the 21st century digital lifestyle paradox: Jekyll and Hyde 2.0. You are going to become more "real" - measured, monitored and optimised - than you've ever been before. You'll know yourself in a way previous generations never could. But you'll also be phonier. More inauthentic, filtered, self-censored and spun than your parents and grandparents could ever have been. And all by virtue of your ubiquitous companion ... the mobile device in your pocket or bag.