"Know thyself," the Oracle at Delphi urged. Easier said than done. Whether in pre-Christian times, the Dark Ages, the Renaissance, the Enlightenment, with the coming of Freud and psychoanalysis, knowing who we really are has remained a tall order, and perhaps an impossible one.

Who is this person looking back at me out of the mirror? It is not necessarily a narcissistic question. And it is probably worth having an accurate answer to it. Robbie Burns famously pointed out what can go wrong when we lack self-knowledge:

Amy Poehler voices Joy in Inside Out
Amy Poehler voices Joy in the film Inside OutWalt Disney Pictures/Pixar Animation Studios

"O wad some Power the giftie gie us
To see oursels as ithers see us!
It wad frae mony a blunder free us,
An' foolish notion..."

To a Louse, 1786

It is, it seems, a permanent feature of the human condition to wonder who we are and what we are really like. This summer's Disney/Pixar smash, Inside Out, takes an extended look inside the head of an 11-year-old girl, Riley, to explore her mixed emotions – in particular Joy, Anger, Fear, Disgust and Sadness. It is coming to something when a children's movie is dabbling in post-Freudian psychology and neuroscience, albeit in a comic and brightly coloured way.

Self-knowledge matters at work, too. Well-intentioned HR interventions, such as 360-degree appraisals, and performance management generally, are meant to help us work more effectively. Mishandled, such interventions probably make things worse. But if we don't explore what might be holding us back how can we improve?

A new piece of research from Korn Ferry, the executive search firm, has cast some light on the question of managers' self-awareness. Over a three-year period, it looked at 7,000 self-assessments carried out by managers at 486 public companies around the world. The aim was to identify "blind spots" – areas where the managers had a higher opinion of their skills and abilities than their colleagues did. The frequency of blind spots was tracked against movements in the companies' share prices.

Korn Ferry found poorly performing companies' professionals had 20% more blind spots than those working at strongly performing firms, and that poor-performing companies' professionals were 79% more likely to have low overall self-awareness than those at firms with healthy share price growth.

In other words, managers in successful businesses had a much clearer sense of what their strengths and weaknesses were than managers in less successful businesses did. This sounds important.

Counter-productive appraisal methods?

But what about the complaint that 360-degree appraisals can be a clunky and even counter-productive way of exploring people's personality and performance? "Any insight is only as good as the data you get," agrees Steve Newhall, managing partner at Korn Ferry. "The data has to be gathered for the right reasons, and delivered well."

This last point should not be overlooked. Of course managers will object to what they might see as "psychobabble", or an unwanted intrusion into personal matters. And there has to be agreement that it is worth doing something about genuine weaknesses.

Canary Wharf
'Managers will object to what they might see as "psychobabble", or an unwanted intrusion into personal matters'Getty

"Some executives are incredibly comfortable with their own bad behaviour," Newhall says. "There are two elements to this: first, do you know what your strengths and weaknesses are, and second, are you prepared to do anything about it?".

I don't know if the homicide inspector Harry Callahan – "Dirty Harry" – would have made a very good manager, but when he declares in the film Magnum Force that "a man's gotta know his limitations" he shows his understanding of at least half the battle.

We need help – candid assessment – from competent people if we are going to get better at what we do. But we also have to be ready to receive those assessments, and act on them.

"Know thyself? If I knew myself I'd run away," German poet Goethe joked. Perhaps full, perfect self-knowledge will always remain out of reach. Perhaps for the sake of our sanity it should. But understanding ourselves better, recognising (accurately) our strengths and weaknesses, and doing something about the latter, has got to be a good idea. It would from many a blunder free us, and foolish notion.

Stefan Stern is a business, management and politics writer. He writes for The Guardian and The Financial Times and is a visiting professor at Cass Business School.