Why do we believe that our job is what makes us worthwhile people?

In the modern world, it's almost impossible to go for more than about a week without having a career crisis, one of those moments (often on a Sunday evening) when the difference between your career ambitions and your professional reality becomes achingly clear.

The central for the reason for the crisis lies in hope, for the oddest thing about the world of office work isn't the long hours we put in or the fancy machines we use to get it done; it's the widespread expectation that office work should make us happy, that it should be at the centre of our lives and our expectations of fulfilment.

The first question we tend to ask of new acquaintances is not where they come from or who their parents were, but what they do - for we presume that we'll thereby to discover the core of their identity.

It wasn't, of course, always like this. For thousands of years before the invention of the Excel spreadsheet, work was viewed as an unavoidable drudge and nothing more, something to be done with as rapidly as possible and escaped in the imagination through alcohol or religious intoxication.

It was only in the middle of the 18th century that people started to argue for the first time that working life could be at the midst of any ambition for happiness.

There was an odd parallel with marriage here (another area where it's hard to avoid regular crises, though they don't tend to be limited to Sunday evenings).

In the pre-modern age, it had widely been assumed that no one could try to be in love and married: marriage was something one did for purely commercial reasons, to hand down the family farm or ensure a dynastic continuity.

The mistress was to marriage what the hobby was to the day job - a way of avoiding the full force of disappointment.

Yet in the mid-18th century, people suddenly started to argue against mistresses and hobbies.

So we are the heirs of two very weird and ambitious beliefs: that you can be in love and married - and in a job and having a good time.

It has become as impossible for us to think that you could be out of work and happy as it had once seemed impossible to an aristocratic age to think that you could be employed and human.

When things at the office are not going well, it's useful to remember the basic point that our identities stretch way beyond what is on the business card, that we were people long before we became workers - and will continue to be human once we have put our tools down forever.

I'm struck by St Augustine's injunction that it is a sin to judge a man by his status. In other words, when work is not going well, we need to remember to distinguish our sense of worth from the work we do.