Sometimes it's not a rational belief, but rather an insecurity brought about by a culture that always took this belief for granted. It's complicated precisely

Sometimes it's not a rational belief, but rather an insecurity brought about by a culture that always took this belief for granted. It's complicated precisely because it's signalling, so in context insecurity over the size of the diamond might not be an actual red flag. You might decide to take a principled stand on the matter, and I agree that insistence on a large diamond is a deal breaker, but not everyone has the same upbringing, cultural belief system, or social environment.