It seems to be a problem of "desired processes" vs "goals". Picking Martha Monkey up from the station is a goal, while playing outside is a desired process. If one Noddy picks up Martha Monkey from the station, all of the Noddys' desires for Martha to be back from the station are fulfilled. However, if a Noddy plays outside, this only fulfills that Noddy's desire to play outside.

This looks a lot like the "tragedy of the commons" idea so often referred to in economics, when framed in the sense of multiple simultaneous instances of the same person. This is the first time I have really understood how TDT works.