The other day I read that a man had pushed a person onto the tracks in front of an oncoming train. 

The week before that, I'd read in a book by Robin Ince that a person who -- having had a baby thrust into his hands -- has intrusive thoughts of throwing said baby out of the nearest window is [believe it, or not] the best person to ask to hold one's baby.

The argument goes like this, the person having these intrusive thoughts is being intensely reminded by his or her unconscious mind that under no circumstances -- no matter what unexpected or unusual events should transpire -- is he to throw the baby out the window (or otherwise do anything injurious.)

I've heard that, at some point, virtually everyone has some type of awkward intrusive thought such as the thought of pushing a stranger in front of a train. 

Most never do it, nor truly want to do it.

Then this one time... someone did.