A system is not something given in nature, but something defined by intelligence... We select, from an infinite number of relations between things, a set which, because of coherence and pattern and purpose, permits an interpretation of what might otherwise be a meaningless cavalcade of arbitrary events. It follows that the detection of system in the world outside ourselves is a subjective matter. Two people will not necessarily agree on the existence, or nature, or boundaries of any systems so detected.
Anthony Stafford Beer (1966, p. 242–3) as cited in: John Mingers (2006) Realising Systems Thinking: Knowledge and Action in Management Science. p. 86.