But we also lie naturally and instinctively, as a way to manage and control our relationships, to protect our partners and our families, and to keep our options open.
In fact, we lie so much and for so many reasons that often we don't even think of it as lying at all, but as 'relationship management'. Those simple, altruistic lies such as saying we've had a lovely time when we haven't, that someone looks nice when she doesn't, or that we're delighted with a gift we don't really like, are just some of the small ways that lying oils the wheels of our social lives, keeps the peace, and makes other people happy.
She has told me and her sister - otherwise, she says, she's '100 per cent certain' that nobody else knows.'I won't allow Mark to call me on my mobile or email me, ever. I insist we talk on our office landlines, and when we meet for drinks or dinner, we pay with cash.
'We work in the same field, so meeting for lunch doesn't look suspicious.
Many women also develop a habit of secrecy about smaller issues in their relationship as a way of maintaining some kind of control.