"Perhaps in future it would be better if all involved accepted the age old adage that private parties are just that." So wrote Nathaniel Rothschild in his now infamous letter to the Times newspaper about George Osborne, the shadow chancellor. Rothschild's letter was short, sharp, punishment, meted out because Osborne broke one of high society's unwritten rules.

Unwritten rules surround us, some we are aware of and others we are not, because they are unconscious. In both cases there are consequences for breaking these rules. For example, stereotypes are powerful sources of unwritten rules. When you think of a leader what sort of person springs to mind? For most of us the answer will be a man, especially a tall man. Take the workplace. Recent research by the Cranfield School of Management showed that women held just 12 per cent of board seats at FTSE 100 companies. Meanwhile, Psychologists have found that tall men earn more than their shorter counterparts - a man who is 6 feet tall earns, on average, nearly $166,000 more during a 30-year career than a man who is 5 feet 5 inches.

This is because women, and short men, break our unwritten rules. We expect our leaders to show signs of 'strength' such as a large stature and a deep voice. However, these examples show that unwritten rules can be neither fair nor helpful. Importantly, we can also fall foul of our own rules. Take Warren Harding who was president of the United States from 1921-1923. In his book 'Blink', Malcolm Gladwell draws on evidence describing Harding as "Looking like a President"; his biographer wrote that his "lusty black eyebrows contrasted with his steel-grey hair to give the effect of force, his massive shoulders and bronzed complexion gave the effect of health." In essence, this was a man who appealed directly to out unwritten rules about what a leader should look like.Unfortunately for the American electorate, Harding has also been described as "one of the worst presidents in American history". His limited intellect and unclear direction meant that he was, in many respects, an ineffectual leader. The voters' unwritten rules blinded them to the rather disappointing reality.

This poses a real problem for organisations that can't (or won't) challenge and change these types of unwritten rules. The result is talent management, promotions, and hiring processes which play to stereotypes, hunches, and 'intuition', favouring those who meet the rules but not the real needs. The result, like Harding, can be someone who looks like they can do a job which, in reality, is beyond them, whilst those who are capable are either frustrated bystanders or are busy succeeding elsewhere. In the current climate who can afford that?