Oh no! The poor Ill Girl with cancer who runs the orphanage is being menaced by the Serial Killer! No one has survived his attacks yet, and it's going to break her fiancé's heart, and after he finally got up the courage to propose to her!
This is when we turn to the writer and say, "Like You Would Really Do It". Much like Yank the Dog's Chain in reverse, this is what Genre Savvy viewers retort when their Willing Suspension of Disbelief is no longer suspended, and in fact falls flat on its back because the writing staff that was supposed to catch it in the "trust building exercise" have wandered off to look at something shiny.
What this means is we don't buy the suspense or anguish that the character is being menaced with, we know the Sorting Algorithm of Mortality has this particular character dead last (pun intended) in terms of who's gonna die, and so we just count the seconds before the door is smashed open and The Cavalry charges in, or the bad guy goes "You're Not Worth Killing". This reaction extends not just to the stunningly innocent, but to any hero or character with thick Plot Armor in a setting where things Could Have Been Messy. Even the Heroic Sacrifice, capable of felling the mightiest of heroes, falls short of really killing them.
Mind, some authors really will call our bluff and kill this character, permanently, and since the vast majority don't it comes as quite a shock when they do. Generally, actually offing a traditionally "safe" character requires a shift in tone for lighter series, but reinforces the Anyone Can Die tone of more cynical works. Of course, taking it too far can create a Moral Event Horizon for the author in the eyes of his fanbase, or it can cause them to stop caring about any of the characters because they'll probably all end up dead anyway.
When actually killed, leads to speculation that He's Just Hiding. See also Narm. Often overlaps with a Disney Death. If it involves whether a hero will win or lose a battle, it's Invincible Hero. If this applies to lesser good characters who might otherwise be killed off, it's Immortal Hero. The Good Guys Always Win is the most common cause. Contrast Audience Apathy.