"Entropy interpreted as a measure of our ignorance about a system"
The essence of the entropy concept. What comes out, freely associated, by this attempt to clarify the energy carried by a system?
As the quest started it addressed a real problem. Energy in a system that can do work, therefore 'useful' and energy that can not do work and as such 'useless' energy. And from that need, the pursuit of finding the ultimate cause of energy's duplicity in occurrence, led to the quantum level, to deal with the microscopic configurations that give rise to the observed macroscopic description of a system. The field is vast, the feat impossible but the tenacious human never gives up.
Up on the task, digs deeper and deeper into the fabric of reality. And in the process invents new concepts, new ideas to explore deeper, in process and in structure. The words in its conceptual arsenal continuously increase, methodically develop to describe and define ever smaller 'nooks and crannies' in the revealed micro-structures and every minuscule detail in subtle, barely perceptible micro-processes.
The discovery process goes on relentless. A lot of concepts and ideas are abandoned as the theories are constantly tested and new sharper concepts replace older ones. The whole process make it possible for the later generations to start their lives on a firmer footing in this world.