In order to an airplane stays in the air is required an strict obedience to some physical laws and principles, for example, the principle of aerodynamic sustentation by which a higher air pressure underneath the structure of the wings happens due to a particular shape of that structure. The moment you disobey this principle, the airplane starts to fall down immediately, no matter what. So, it is part of the essence of flying an airplane.
Definitively not in the same physical vein, but for the sake of illustration I would say —based on my observations— that part of the essence of an agile software development environment is the actual presence of business people that care their project enough that they expect, are eager to, and actually do take advantage of the management powers of the learning and discovery experience of iterative and incremental development, exploiting the wealth of information flow that comes from the development team as well as from the business domain, taking critical and needed business decisions eagerly, given clear and constant business direction to the development team which in turn refocus development effort accordingly new corroborated business information. Negotiations, feature set, efficient resource management, customer satisfaction, profits, etc., could be improved by means of people with a clear understanding of the business-enabling scenarios of an agile mindset.