As Wimbledon has just ended, it feels appropriate to discuss the subject of unforced errors. I’m not referring to shots on a tennis court: I’m talking about big, self-inflicted mistakes that can undermine a commercial career – or indeed an entire life.

● The most common destructive behaviour that obliterates success is alcoholism. It shortens lives, causes immense collateral damage, and gradually asphyxiates even the greatest talents who fall victim to liquor’s awful spell. George Vaillant, director of the Harvard Grant longitudinal study – which has followed a cohort of college students since 1938 – states in his book Triumphs of Experience that alcohol abuse is the largest preventable disrupter of health and happiness. I have seen high achievers slide into havoc through booze: neither education nor intelligence are insurance policies against it.

● Personal guarantees are similarly toxic in business . Debt is usually necessary if you are highly ambitious and want to build a big business, and retain a large piece of it. But one should remember to take full advantage of the limited liability system, and not put one’s solvency on the line, whether for a loan, lease or any other obligation. Last year an old friend, who was a multimillionaire only 10 years ago, was declared bankrupt because he spent too much, backed the wrong companies – but principally because he had guaranteed borrowings.