When we're caught doing wrong, we try to make amends and restore others' good opinion of us. But what about when we're already in moral credit?
In one Canadian experiment, volunteers split into two groups. The first received money to buy items from an environmentally-friendly store: energy-saving lightbulbs, organic crisps, natural deodorant. The second spent their allowance in a shop where products were marketed on taste and efficacy rather than boosting your environmental credentials.
In Toronto, buying green is a virtue. The first group had done their good deed for the day.
After selecting their groceries, both groups took part in a `visual perception task'. The task was easy to cheat. The volunteers then paid themselves from an envelope based on their performance.
Those who'd done their bit for the world felt licensed to take a little back. They cheated more on the test, and on average took an extra fifty cents from the envelope.
Toronto students aren't unusual. It's a common finding that being a little good allows us to be a little bad:
People who reflected on their less pleasant qualities donated more to charity than those who first wrote about their more positive traits
Obama supporters who received a chance to endorse the then candidate were more likely to choose a white officer as police deputy than Obama supporters who didn't first get to demonstrate their non-racist attitudes
It's important to us that we're perceived as moral people, that we behave in an acceptable way. But few of us are aiming for sainthood.
Bill Gates operates an aggressive monopoly but donates to charity. Trump grabs women but is affectionate towards his children. Gandhi fought apartheid and colonialism but insisted young women slept in his bed. Most of us balance our moral accounts on a far smaller scale.
If you want someone to do you a favour, you might be tempted to approach those who have a reputation for benevolence. But you could do better searching for someone with a less salubrious image. And if a friend tells you about her charitable giving and green purchases, don't leave her alone with your valuables.
Dr Chris Paley is the author of Unthink, which has been published in six languages. One reviewer said it would 'make you happier than a rabbit on a carrot farm'. Buy it here if you want to be that happy.