"It's a commonplace of parenting and modern genetics that parents have little or no influence on the characters of their children. You never know who you are going to get. Oppotunities, health, prospects, accent, table maners - these might lie within your power to shape. But what really determines the sort of person who comes to live with you is which sperm finds which egg, how the cards in two packs are chosen, then how they are shuffled, halved, and spliced at the moment of recombination. Cheerful or neurotic, kind or greedy, curious or dull, expansive or shy and anywhere in between; it can be quite an afront to parental self-regard, just how much of the work has already been done. On the other hand, it can let you off the hook.
The point is made for you as soon as you have more than one child." Ian McEwan, Saturday