There is nothing that a single massive sphere will or can ever do by itself that says it will both exert and yield attractively with a neighboring massive sphere and that it yields progressively: every time the distance between the two is halved, the attraction will be fourfolded. This unpredicted, only mutual behavior is synergy.
103.00 - Synergetics: Explorations in the Geometry of Thinking (1975) - "Synergy" onwards