The saying is annoying enough. Grenna finds herself hearing it all the time and it drives her insane. At some point it's actually put into literal terms as Grenna's life is turned around.
"Your blood is the only way to cure vampirism."
"That's-that's impossible."
"Not when your real mother is a Bennet witch."
*if you've watched seasons 3+ of tvd skip until chapter five*