This is not an uncommon trajectory. Many people think that they have a set type, and that all they need for eternal bliss is to find someone who matches it. When people peruse dating profiles, they’re often looking for someone who has specific interests, qualities, or hobbies. But according to a growing body of relationship research, many people end up marrying someone with few of their must-haves and a lot of “haves” they didn’t think they desired. A person might say that they’re looking for a partner who’s funny and conscientious, but then end up in a happy relationship with someone who is neither of those things. “People don’t know what they want,” Samantha Joel, a psychologist at Western University in Ontario who studies relationships, told me, “and people don’t know what they’re going to like until they meet someone.”