Answer:
Lying is probably one of the most common wrong acts that we carry out (one researcher has said 'lying is an unavoidable part of human nature'), so it's worth spending time thinking about it.
Most people would say that lying is always wrong, except when there's a good reason for it - which means that it's not always wrong!
But even people who think lying is always wrong have a problem... Consider the case where telling a lie would mean that 10 other lies would not be told. If 10 lies are worse than 1 lie then it would seem to be a good thing to tell the first lie, but if lying is always wrong then it's wrong to tell the first lie...
Acknowledgement
Nobody who writes about lying nowadays can do so without acknowledging an enormous debt to this groundbreaking book: Lying: Moral choice in public and private life, by Sisela Bok, 1978.
