When can I go from thwarting, to destroying?
For example, say the protagonist was working towards a goal, but towards the end they killed the people they had spent the novel with, as they became so obsessed with the desire and didn't want to be stopped. The threat was not destroyed, their friends were dead, and they were left to well, be insane.
Would doing something like that be way beyond thwarting the readers hopes, and destroying their enjoyment of the novel? Its pretty obvious that the protagonist would reach their goal from the start, so, I was thinking about destroying it. Is going to that point too far, or would it be more sensible to let them have their goal, but at a price?