You cannot sum up the behavior of the whole from the isolated parts, and you have to take into account the relations between the various subordinate systems which are super-ordinated to them in order to understand the behavior of the parts.
p. 68 cited in: T.E. Weckowicz (1989). Ludwig von Bertalanffy (1901-1972): A Pioneer of General Systems Theory. Working paper Feb 1989. p. 2 - General System Theory (1968) - 3. Some System Concepts in Elementary Mathematical Consideration