As somebody who's been in a situation similar to this (fortunately they never got as far as pulling the knife because I stopped traffic), I still find it hard to blame people who don't help - you need to know where to draw the line in help, and it's a very blurry line. Your personal experiences are sadly biased; more than one helpful person has ended up dead because they were out of their depth [1][2][3]. As you say, such is life.