Large Systems and the chaotic interaction between their parts can be readily modeled by numerous distinctions which message each other in such a way that, given an initial condition and enough time, the outcome of the system’s evolution will be completely determined by the characteristics of the interaction between the distinctions.
In Smalltalk, everything is a distinction and everything that happens is a message send. Because of this, Smalltalk is an extremely suitable environment in which to model complex systems and their emergent properties.
This key observation will be tacitly used to let behavior occur as an emergent property of objects and their interactions, as opposed to giving commands and issuing orders. This change of perspective, even though delicately subtle, is of the utmost importance.
The art of object oriented programming is the conscious and careful design of the pieces such that the desired outcome is an emergent property of the whole.
This book is an attempt to illustrate this distinctive and artful way of building programs, how it can become second nature for you, and how you can obtain valuable results by using it.
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Section 1.3.2 of A Mentoring Course on Smalltalk, Large Systems