From FreeSpace Wiki
Mission Goal Incomplete (Boolean operator) Returns true if the specified goal in the this mission is incomplete. This sexpression will only be useful in conjunction with another sexpression likehas-time-elapsed. Used alone, it will return true upon misison startup.Returns a boolean value. Takes 1 argument... 1: Name of the event in the mission.
Don't use this for debriefings. All mission goals that are incomplete upon jump-out will turn to false.