Why are people drawn to things they FEAR?

An example of this would be someone who becomes glued to or mesmerized by a video of some awful event like a really bad building fire or traffic accident. I had some friends over the other day and someone found that terrible video of The Station nightclub fire online. I don't understand why some people get stuck to that video (and keep watching) even though they say they didn't want to watch it. Anyone know the answer?

I do NOT mean someone who "enjoys" being scared.

I would venture a guess that it could be instinct or shock... but don't know. I personally turned away and am glad I did.