I find it much easier to be highly productive when I have loads to do and am balancing multiple things at once. I find it much more difficult to do anything when my task list, or even my 'want to list', is short. I haven't figured out why this is yet. Parkinson's Law maybe?
Maybe it's similar to how light bends due to space curvature. Our 'mind' is always flowing forwards in the river of the time but we can steer it towards invisible (upwards, downwards, flat) topographies that are (tiring, exhilarating, boring.)