This is actually a well known phenomenon (http://en.wikipedia.org/wiki/Bystander_effect http://en.wikipedia.org/wiki/Bystander_effect). It's why, in a crisis,

This is actually a well known phenomenon (http://en.wikipedia.org/wiki/Bystander_effect http://en.wikipedia.org/wiki/Bystander_effect). It's why, in a crisis, you should always single people out to do tasks instead of saying "someone do this". Otherwise everyone will just assume that someone else will do it.