Anyone who has even the slightest amount of self-doubt knows the feeling of walking into a party to find someone else is wearing the exact same dress. If you grew up with a sibling, you know the pain of wearing the same sweatshirt on the same day and fighting about who needs to change. No one wants to look like they are copying someone else in an attempt to look cool. So you have to be really, really close with someone as well as confident with yourself to try a matching trend together on purpose.
Mila Kunis and Kristen Bell are that close.