Private enterprise has quite a lot in common with medieval kingship – the ruthless struggle to increase wealth and holdings in spite of the near certainty that what is built up by a strong leader will be lost by his weaker successors.

Amid all this depressing impermanence, there is also a mystical, more enduring concept of kingship, best illustrated by John Boorman’s bloody but brilliant film Excalibur: “The land and the king are one”.

This might sound like airy-fairy nonsense, but a brief glance at the history of the Hundred Years War or the Wars of the Roses will confirm that a strong, vigorous king was more likely to preside over a strong, vigorous kingdom. If, on the other hand, the king was an infant or mentally infirm, his realm would be torn apart by competitors.

So it is in modern business. “The entrepreneur and the business are one”.

If an entrepreneur is full of energy and ideas, the same will be true of his business. It will be expanding. It may sometimes suffer setbacks where its optimism overwhelms good judgement, but that same optimism will enable it to recover quickly.

If, however, the entrepreneur is lethargic, the business will lose its edge. Employees take their cue from the boss. No one who owns a business should expect those with less of a stake in it to take up the slack if he becomes apathetic.

All this brings us to a point we have often made before, but one as old as kingship: an entrepreneur’s business depends on his personal health, and his health depends, in turn, on a balanced lifestyle.

Medieval kings did not live like medieval monks, so the entrepreneur should not be a monomaniac – he should not be obsessed with his business or his personal health. All the science suggests that obsession destroys both its subject and its object. The ideal is instead to develop a virtuous circle in which a healthy personal life leads to a healthy business life, and a healthy business life provides the funding and security necessary for a healthy personal life.

While some activities are innately unhealthy, many of the things that are called “vices” are nothing of the sort – they are bad only in excess. Food and sleep, for example, are biological necessities: they turn into Gluttony and Sloth respectively only when they are taken to an unnecessary extreme. At that point they become counter-productive: instead of sustaining the body, they destroy it. The same is true of business itself. Obsession is unprofitable.