It's a trope near and dear to our hearts. Arranged marriage.
Maybe it's for the family. Maybe it's for a friend. Maybe you know the person and have been expected to marry them for years. Maybe it's the wedding day and you have no clue who it is you'll be tied to for your natural life. Maybe you've been married a while, and you're just now starting your life, away from the expectations of others. Or maybe, the "others" are watching, waiting, making sure this marriage sticks.