This idea is known as “the self-fulfilling prophecy". When you believe the team will perform well, in some strange, magical way they do. And similarly, when you believe they won’t perform well, they don’t.

There is enough experimental data to suggest that the self-fulfilling prophecy is true. One unusual experiment in 1911 concerned a very clever horse called Hans. This horse had the reputation for being able to add, multiply, subtract, and divide by tapping out the answer with its hooves. The extraordinary thing was that it could do this without its trainer being present. It only needed someone to put the questions.

On investigation, it was found that when the questioner knew the answer, he or she transmitted various very subtle body language clues to Hans such as the raising of an eyebrow or the dilation of the nostrils. Hans simply picked up on these clues and continued tapping until he arrived at the required answer. The questioner expected a response and Hans obliged.

In similar vein, an experiment was carried out at a British school into the performance of a new intake of pupils. At the start of the year, the pupils were each given a rating, ranging from “excellent prospect" to “unlikely to do well". These were totally arbitrary ratings and did not reflect how well the pupils had previously performed. Nevertheless, these ratings were given to the teachers. At the end of the year, the experimenters compared the pupils’ performance with the ratings. Despite their real abilities, there was an astonishingly high correlation between performance and ratings. It seems that people perform as well as we expect them to.

The self-fulfilling prophecy is also known as the Pygmalion Effect. This comes from a story by Ovid about Pygmalion, a sculptor and prince of Cyprus, who created an ivory statue of his ideal woman. The result which he called Galatea was so beautiful that he immediately fell in love with it. He begged the goddess Aphrodite to breath life into the statue and make her his own. Aphrodite granted Pygmalion his wish, the statue came to life and the couple married and lived happily ever after.

The story was also the basis of George Bernard Shaw’s play “Pygmalion", later turned into the musical “My Fair Lady". In Shaw’s play, Professor Henry Higgins claims he can take a Cockney flower girl, Eliza Doolittle, and turn her into a duchess. But, as Eliza herself points out to Higgins’ friend Pickering, it isn’t what she learns or does that determines whether she will become a duchess, but how she’s treated.

“You see, really and truly, apart from the things anyone can pick up (the dressing and the proper way of speaking and so on), the difference between a lady and a flower girl is not how she behaves but how she’s treated. I shall always be a flower girl to Professor Higgins, because he always treats me as a flower girl, and always will, but I know I can be a lady to you because you always treat me as a lady, and always will."

The implication of the Pygmalion effect for leaders and managers is massive. It means that the performance of your team depends less on them than it does on you. The performance you get from people is no more or less than what you expect: which means you must always expect the best. As Goethe said, “Treat a man as he is and he will remain as he is. Treat a man as he can and should be and he will become as he can and should be."