Why do we freak out when we KNOW for a fact that the main character doesn’t die (he/she’s in the next installment’s blurb), or that a happily-ever-after is pretty much guaranteed (i.e. paranormal romance, contemporary, etc)? I think it’s because as readers we become so invested in the characters that when something bad happens to them we take it to heart. Personally, when I’m engrossed in a novel, I’m more of a live-in-the-moment kind of gal, meaning that I’m just enjoying the ride the way that the author intended, so when those oh shit moments happen I’m not thinking about the eventual HEA. My whole world becomes that thing that made me freak out/worry/cry like a baby.
Plus, in my opinion if an author can make you feel all of those things, then mission accomplished!