In a perfect world, every wedding ceremony and reception would go off without a hitch.
No one would trip on their big walk down the aisle; the florist wouldn't call with some sort of last minute bouquet-related problem; that uncle you really didn't want to invite but your mother made you invite anyway wouldn't show up to the dinner with his 19-year-old date, ready to cause problems with his estranged wife who thought he wasn't going to be there.
But sadly, this isn't a perfect world, and murphy's law is kind of a b****.