Suppose the player's mother is supposed to be cleaning the living room, but she can be interrupted by the need to pick up things the player has dropped. New tasks are added to the end of her "current plan" list; every turn, she attempts to do whatever is the last entry on that list.
say "Your mother picks up [the noun][one of], sighing deeply[or], jaw tight[or], with assorted comments on your manners[or]; to judge from her comments, she is also indulging in a pleasant fantasy about Swiss boarding schools[stopping]." instead.
When play begins:
add mother going west to the current plan of mother;
add mother rubbing the rug to the current plan of mother.
Every turn:
if mother is not in the Living Room, end the story finally.
As goal-seeking goes, this is fairly rudimentary; "Boston Cream" provides an alternative (and slightly more sophisticated approach), but for really complex goal-seeking characters, it is probably best to turn to the character extensions designed for Inform.