Dr Sandra Murray and psychologist colleagues at New York State University have published a series of studies in recent years that attempt to get to the bottom of whether we stay with the person we are married to because we see them in an inaccurately positive light. The theory is that being relatively blind to their faults and vices helps us live with them and keeps the marriage going for much longer than if we were more aware of their flaws.

The psychologists compared what spouses thought of each other with the opinion of very close friends and others who knew the spouse well.

The key finding is that highly satisfied spouses tend to see more virtue in their partners than their partners perceive in themselves. This becomes more impressive when you consider that most of us tend to regard ourselves in an overly positive way.

Spouses also rated themselves much more positively on various personality features than their own friends did.

Dr Murray concludes the reason these illusions about partners are so common in sturdy marriages is that, to be happy, we need to believe we are in the right relationship with the right person.

However, sustaining this belief in the face of partners who sometimes disappoint seems to require the buffer of perception of special virtues. Once achieved, argues Dr Murray, this positive perceptual bias allows people to dispel potential doubts.

After all, few decisions have higher stakes than the decision to commit to one partner. To feel happy and secure in the face of such vulnerability, we need to believe our relationship is good and our partner can be counted on to be caring and responsive.

There is a sense in which the different professions that attempt to work together in the NHS can be seen as trying to make a difficult marriage work.

Could it be the only way we are going to avoid an acrimonious divorce is for us to harbour positive illusions about each other? Does this also explain why so many hospital doctors drift into the infidelity of private practice, research, medical politics or basically anything but the burden of 'seeing the wife'?

Dr Raj Persaud is consultant psychiatrist at South London and Maudsley trust and Gresham professor for public understanding of psychiatry.