In an article discussing collaborative spam filtering and the Tor project, Bruce Schneier offers some refreshing advice: telling children not to talk to strangers isn’t strictly the best advice:
When I was growing up, children were commonly taught: “don’t talk to strangers.” Strangers might be bad, we were told, so it’s prudent to steer clear of them.
And yet most people are honest, kind, and generous, especially when someone asks them for help. If a small child is in trouble, the smartest thing he can do is find a nice-looking stranger and talk to him.
These two pieces of advice may seem to contradict each other, but they don’t. The difference is that in the second instance, the child is choosing which stranger to talk to. Given that the overwhelming majority of people will help, the child is likely to get help if he chooses a random stranger. But if a stranger comes up to a child and talks to him or her, it’s not a random choice. It’s more likely, although still unlikely, that the stranger is up to no good.
I suppose it’s a form of the selection bias.