People frequently reveal information about others, deliberately or inadvertently, through the lifestream. Someone without a Twitter account can be referenced in a tweet. A person who chooses not to check in at a bar can still be photographed by another patron. Someone can be tagged in a photo on Facebook even if they do not have a Facebook account. Two users who are not directly connected through social media site may appear in each other’s streams through mutual friends.

Alice E. Marwick, Status Update, loc. 637