The theory when you give a lady a pair of expensive designer shoes (e.g. Christian Louboutin, Jimmy Choo or Salvatore Ferragamo) she is willing to do any (sex-related) actions for the next 24 hours.
Hey Joe, you look like you had some last night. Hey bro, my lady bought some Lou's yesterday and thus the Louboutin-window kicked in so she sucked my cock this morning.