Next week, mums across the country will likely fight back tears at the school gates. 

Or, if they manage to hold it together, they cry in the car afterwards. Or in the kitchen while shakily making a cup of tea. Or, in my case, into the neck of a long-suffering miniature dachshund while he enthusiastically licks the tears from my face and I let myself believe this is his way of empathising. (He actually just really likes salt.) 

We've ironed the uniform, laid out the comically oversized new shoes and taken the obligatory first-day-back photos for The Gram. Now we're watching our children disappear into new classrooms looking somehow so much older than they did when they came tumbling out just six weeks ago. Another summer gone. Another milestone reached. Another reminder that the clock is ticking on their childhoods.  

Nobody thinks anything of these tears. If anything, they're considered rather lovely. They're taken as evidence that our maternal instincts are in good working order. They don’t make us look less capable. If anything, they make us look like we're getting motherhood exactly right. Well done us. 

Yet when Rachel Reeves cried in the House of Commons earlier this summer, evidently the same rules didn't apply. 

"Tears AGAIN!" sneered a tabloid. 

The implication was clear. These weren't the acceptable tears of a devoted mother. They were evidence that the then Chancellor wasn't coping. 

Rachel Reeves has become the latest poster girl for the idea that tears and professional competence cannot co-exist. Her emotional moment was picked apart in the tabloids. The rest of us might get away without the headlines, but don't we half do the job ourselves, conducting our own internal performance appraisal? Did anyone notice the sniffles, the streaky mascara? If so, what did they conclude? She's not resilient enough? Tough enough? Authoritative enough? She clearly can't separate emotion from professionalism (as though those two things sit at opposite ends of a spectrum). Even if nobody else is thinking those things, there's every chance we're thinking them about ourselves.

The internationally adored Katy Perry learnt a similarly unfair lesson last year. Weeks after online pile ons about her tour's budget and a widely mocked trip to space, she stood in front of thousands of adoring fans and cried. Some called it strength, others thought she’d brought it on herself. Nobody said she shouldn't cry. The global audience just couldn't decide if it counted against her. 

Somewhere along the way, we've all internalised the unofficial decoder guide to tears. Missed that particular memo? It goes something like this: 

Cry at the school gates = loving mum. You’re winning.  

Cry at your child's graduation = pride. Great job.  

Cry at a funeral = grief. Totally understandable. 

Cry because your team has just made the final = passion. Whoop! 

Cry because they've lost = devotion. There, there. 

Cry in the office = incompetence. Uh-oh.

The same physiological response attracts a completely different verdict the moment it happens anywhere near the office. The trouble is, it's not like we can help it. We can no more stop the tears coming after a clash with the boss than when those little hands slip from ours at the start of a new term. It’s not like anyone ever walked into a difficult meeting thinking, "The best possible outcome here is a good sob." If anything, we'll do everything in our power to stop it happening. We'll stare at the ceiling. Bite the inside of our cheek. Hold our breath. Scribble a few choice words on the meeting agenda. Excuse ourselves to the toilets. Anything to hold in the emotion that, in this particular setting, we've somehow been taught could earn us, if not a P45, then at least a whole host of negative insinuations about our abilities. 

The irony is that our bodies couldn't care less about any of these rules. Emotional tears are driven by the autonomic nervous system – the bit of us that keeps our heart beating, our breathing going and our pupils dilating without us ever having to think about it. When we're overwhelmed, that system doesn't just process what's happening emotionally; it responds physically too. Think of it as a pressure valve; once things build beyond a certain point, something has to give. Tears are one of the ways the body lets off steam. We don't choose them any more than we choose to blush, yawn or get goosebumps. 

Which makes it all the more absurd that we've attached such wildly different meanings to tears depending on where they land. 

The tears themselves don't know whether they're falling onto a playground pavement, a church pew or the carpet tiles in Meeting Room 3. They don't know whether they've arrived after saying goodbye to a child, saying goodbye to a loved one or sitting through one insufferable meeting too many. Yet we've decided unequivocally what they mean. Only humans could look at bodily fluids and conclude someone isn't leadership material. The dachshund, for one, has seen me cry countless times and still seems convinced I'm absolutely smashing life.

The curious contradiction is that, broadly speaking, we've embraced the ideas of authenticity and vulnerability. Yet visible emotion still seems to be the one part of ourselves we're expected to keep firmly under wraps. 

I'm certainly not suggesting the office should become one long communal sob-fest. But if exactly the same physiological response can be read as proof that we're getting motherhood right one minute and evidence that we're getting our jobs wrong the next, then aren't we asking women to perform an impossible trick? To be authentic, but not too authentic. To bring our whole selves to work, but not the parts that might make other people uncomfortable. To be warm, empathetic leaders who somehow never have an involuntary human response to an involuntary human moment.  

Isn’t it time we stopped treating tears as a performance metric? They're not evidence of incompetence, weakness or fragility. They're simply evidence that we’re human.