This persistent injustice is also a waste of talent – and men as well as women need to see why before we can change it, says Tom Schuller

Sociologists, economists and many others have analysed exhaustively why women don’t get certain types of job or progress beyond certain levels, and why gender pay gaps exist.

That the competence gap between women and men is increasing, in almost every developed country, gives added salience to the question: how and why is women’s competence not recognised and rewarded as men’s is? That competence gap is increasing faster than the gap between men and women’s pay is closing. There is a striking mirror-image symmetry here with the famous (or once famous) Peter Principle, that “Every employee rises to his [sic] level of incompetence.” The opposite is the Paula Principle: “Most women work below their level of competence.”

This principle reveals two things that should concern us all: a persistent unfairness or injustice in the way education is rewarded; and a waste of proven talent. By “rewards” I don’t mean only financial returns, but also satisfaction from knowing that one’s abilities are being properly employed, and a sense of progression, of moving forward.

As a man writing primarily about what is and isn’t happening to women at work, at times I struggle to find an appropriate voice. Obviously I can’t speak with the kind of subjective experience that may give a richer tone. But my intention is to include everyone in the conversation. Indeed, my main conclusion concerns men as much as women. It is that women will only get to use their competences fully when both are able to pursue “mosaic” careers which do not conform to the conventional model of full-time continuous employment.

The competence gap between the sexes is increasing faster than the gap between men and women’s pay is closing

We all need to see equality in a more dynamic way that does not focus only on individual times in women’s working lives, but across their whole life course. Concentrating on symmetry between women and men at any single stage in life is not the best way to frame the issue. For young women with a good educational record, the Paula Principle may no longer seem to apply: the pay gap for them is likely to be minimal, and most options are open to them. But will this parity last as they get older? Almost certainly not, on current form. Women’s career paths are flatter and more broken, their salaries lower, and their retirement incomes smaller.

In the debate on gender equality at work, there is also a natural tendency to focus on the top jobs: on how few women are judges, CEOs, cabinet ministers and so on. Concentrating on the glass ceiling is understandable, and justifiable in that inequality at this level reflects the structure of power most acutely. People in top jobs are the ones who wield most influence, and so we should be most interested in how they are distributed between women and men, as well as across other social categories. But this excludes the great majority of women, for whom the glass ceiling is not an image that ever resonates.

The Paula Principle applies as much to the clerk who does not apply for a supervisor’s job because she does not have the confidence, as it does to the deputy CEO blocked from the top job by covert discrimination or male cliquery.

It is a system-wide – or, rather, system-deep – principle, not the top layers only, that we need to focus on if we want to see real change.

The Paula Principle: How and Why Women Work Below Their Level of Competence by Tom Schuller is published by Scribe at £14.99. To order a copy for £12.72, go to bookshop.theguardian.com