Okay, believing that the examples above are very much tongue-in-cheek, a comment from the world of screenwriting:
"How can love be a good thing when it hurts more than helps?"
Is not a hook. It is a tag line, the kind of thing a marketing department comes up with to put on the one sheet (movie poster). It is not the sort of thing that makes anyone want to see the movie (or request a partial) because it doesn't mean anything. It could apply to a thousand different books or movies or TV shows. It sounds like a line of dialogue from Friends.
A hook is the one line that describes your plot and makes your would-be reader or viewer or agent say "that's interesting, I haven't seen that before, I have to know how that story turns out." A hook, in other words, is high concept. These are terribly done, but you get the idea:
-A young boy discovers he's a wizard and is sent to a secret wizarding school where he learns he's the only survivor of a deadly spell.
-A girl returns to her family home to find a cure for a curse that is causing her feet to turn to glass.
-A five-year-old boy raised in a single room must escape from the man who has held him and his mother captive.
-A young woman falls in love with a man who travels through time uncontrollably.
All are novels, obviously, and most literary fiction. It can be done. A hook is what is driving your book, the underlying question that must be solved. At their best, they give the reader an idea of a unique problem that is big enough to drive an entire plot and get them started thinking about how they would handle the same issue.
As a side note, it's not necessary to have a high-concept hook. In a novel they can be much softer:
-A young man rides his horse away from his troubled family and tries to build a new life in Mexico.
-A man tries to reclaim the love of his youth, having waited sixty years for his beloved's husband to die.
Note that these softer plots may be of less interest from a beginning writer. An agent reading your query letter might not trust that an unknown writer will have the chops to pull those two stories off as well as Cormac McCarthy and Gabriel Garcia Marquez.
In short, a good hook makes an agent think your book can be marketed, has a target audience, and will sell.