I think context is important - think power laws, faultline stress in plate tectonics, or as in this case magnitude of movement when the move actually comes. As

I think context is important - think power laws, faultline stress in plate tectonics, or as in this case magnitude of movement when the move actually comes. As to what triggers the move itself - my feeling is that some kind of crowd effect occurs, i.e. once we get over some resistance level, then the movement implied in the imbalances described by the context takes over; the crowd creates its own impetus. But it is very difficult or even impossible to determine ahead of time what minor movement will become the catalyst, in much the same way that determining which butterfly flap vortex will become a hurricane.