What could possibly go wrong?
What can go wrong should be contingent on our plot. There are plenty of things that can go wrong that fail to advance the plot. I think I’ve used this example before, but we could have one of the characters die. In a romance, that would be a problem if the dead character is the guy the girl is to fall in love with. My point is that we want bad stuff to happen, but we need to be selective.
When is the worst possible moment?
Going back to the dead guy, we could have him break up with his girlfriend and then drop dead. That would be convenient, but not very interesting. A better approach would be for him be down on one knee proposing, when he is shot in the back or maybe he is driving his girlfriend somewhere when he dies behind the wheel. It should also be on a curvy road with an eighteen wheeler coming from the other direction. Now things are a little more interesting.