When I graduated from college in 1977, the world was still neatly divided into two spheres — work and everything else. Work was supposed to be a hyperrational realm of logic, filled with time tables, organisational charts and returns on investment. It was only outside of work that emotions, were supposed to emerge.

But from the first day of my first real job, as an administrative assistant at the Park Avenue headquarters of a commercial bank. I realised that emotions were simmering everywhere in the workplace.

My desk, on the hushed, deep-pile-carpeted executive floor, was a few feet opposite the restroom doors. Every few days, one of the three executive women on my half of the floor would rush into the restroom and, after a little too long, emerge with the remnants of a good cry still visible on her splotchy face. I also watched men dash into the men’s room and leave a few minutes later, tight-lipped and ashen.

Even as a 21-year-old workplace neophyte, I realised that emotion is a force that underlies our behaviour. For my book, It’s Always Personal: Emotion in the New Workplace, I spent two years exploring Americans’ emotions at work today, and my findings suggest this amended version of Descartes’ famous line: I think and feel, therefore I am.

In the past — pre-Internet, pre-mobile phones — it was a lot easier to believe “work equals rational” and “home equals emotional.” But now that work and home life constantly bleed into each other. People text and email their friends and family members throughout the workday, and they receive messages from colleagues and clients on nights and weekends and during vacations.

The membranes between private life and work, have always been porous, but today employers and employees expect accessibility and accountability pretty much round-the-clock. And whereas old-school office memos and business letters generally weren’t expected to be friendly or candid but business emails most definitely are.

Conversely, what used to be considered private behaviour can instantly reverberate at work through social networking. People fire off emails late at night, only to regret their tone and intent in the morning. Facebook friends from work can stumble upon wild and crazy pictures from a bachelorette party. Tweets and anonymous mobile video uploads can instantly broadcast unflattering emotional displays by surly customer service employees. The conventional wisdom used to be that we brought home the emotions we couldn’t express at work — snapping (or worse) at blameless partners and children. That is still true, but what’s new is that home life, with all its messy, complicated emotional currents, has become inextricably and undeniably woven into the workplace.

The rulebook for modern office etiquette has yet to be codified. How do we avoid hurting one another’s feelings if everything is supposed to be rational, yet also transparent and accessible? How can others understand the emotion behind what we’re trying to say in an email if no one takes the time to read beyond the subject line and the first sentence?

And the more we relegate communication to the electronic realm, the greater our longing for face-to-face contact. Our new “flat” organisational structures at work might seem to promote a more hang-loose level of emotional expression.

No one is sure where the lines are anymore. Should we high-five a newcomer? Is it cool to make jokes with the boss? What if we overhear the man in the next cubicle crying?

Clear rules for this new working world simply don’t exist. But one thing is certain. The millennials, a generation raised with the 24/7 naked emotional transparency of texting and social networking, is now entering the workforce by the millions each year. As they replace old-schoolers born in the 1940s and ’50s, there is no turning back to a compartmentalised world.

I like to imagine that if men and women were to express more emotion routinely and easily at work — jokes, warmth, sadness, anger, tears, joy and all of it — then as a people we might not feel so chronically anxious and overwhelmed.

By denying the range of emotional expressiveness intrinsic and appropriate to the workplace, we find ourselves at a loss for how to handle this brave new boundary-less world.