[gillyb]

I feel that's a little like saying 'Everyone is unique, so psychologists are useless'.. Although everyone IS truly unique, there are still common patterns that emerge, and many commonalities in our upbringings.

We don't act completely randomly, not as children and definitely not as adults. We exist within a common environment with a common set of laws or norms that most people live by (excluding extreme cases, for various reasons).