Everybody picks their nose, neglects on occasion to pick up their dog’s poo, and now and then rolls their eyes at the behaviour of a loved one, usually with affection.

These are mundane crimes, with no great harm done.

Psychologists sometimes like to investigate the mundane and see if it is truly harmless.

But when marketing and business schools start poking around in human nature, they’re not just investigating people with families and occasional foibles, they’re sizing up consumers.

So it goes with a new study, published in the Journal of Consumer Psychology from the Indiana University Kelley School of Business.

Its title is vaguely juicy: ‘Secret consumer behaviours in close relationships’.

Is this breaking a sacred trust?

In this new paper, the authors suggest that close relationships are often characterised by openness and disclosure.

They shoot down that dream by proposing ‘‘there are times when individuals choose not to tell close others about their consumer behaviour, keeping it a secret’’.

They give examples of this deceit: One partner may eat a candy bar on the way home from work; hide a package that was delivered to the house, or hire a cleaning service and not tell the other partner.

And they assert the obvious; this happens all the time and is ordinary human behaviour.

Here’s the real quirk

Most of the time, probably routinely, these same sorts of purchases are made ‘‘with the partner’s knowledge in the past’’.

But on this occasion, they’re being kept intentionally from the partner.

What is the point of it? A re-asserting of one’s privacy? A sly up-yours to your beloved, just for the hell of it?

Or is it because you can’t be bothered explaining every damn thing you do?

The researchers, including teams from the University of Connecticut and Duke University, were not interested in why people keep a secret stash of biscuits or cardigans.

They wanted to know ‘‘whether such behaviour has downstream effects on the relationship, despite its mundaneness’’.

What’s the fallout?

The story has a happy ending.

The researchers concluded that these secret purchases, even if it is just a slice of pizza, are beneficial for the relationship.

Why? Because the sly behaviour ‘‘can lead to slight feelings of guilt but also can drive people to want to invest more in their relationships, which is a positive effect’’, researchers said.

And here the business school part comes to the fore: ‘‘That ‘greater relationship investment’ might include spending more on Valentine’s Day for their partner or being willing to watch their partner’s favourite movie, for example.’’

In other words, secret-spending guilt leads to even more spending purchasing as a means to assuage the guilt.

Ker-ching!