House MD, episode 2-15 : Clueless
Maria: Marriages dont fail because couples get bored. They fail because, while theyre dating people pretend to be the person they think their partner wants and then, well, theres only so long you can keep that up.
Cameron: Maybe they are that person while theyre dating, but then they change.
Maria: People thinking that their partner will change, thats another reason marriages fail. People dont change. Least, not in any way that really matters.