This is Essay 4 of the Collection of 'Essays on Cognitive Physical Science' in the repository UPSpace of the University of Pretoria.Essay 4 is the first of a number of essays focussing on certain key aspects of the author's model of mind, first described in Essay 3 (hdl.handle.net/2236/50310) and again in updated - and currently only relevant - form in Essay 3.1 (hdl.handle.net/2236/58202). The Least Effort Principle is a key aspect of prime importance of the model of mind and is the main theme of Essay 4.