Eliyahu M. Goldratt, What is this thing called THEORY OF CONSTRAINTS and how should it be implemented, North River Press, 1990.
Let's start by calling the desired objective "A". In order to reach "A" we must satisfy two different requirements, "B" and "C", where the prerequisite to satisfying "B" is "D" and the prerequisite to satisfying "C" is the opposite of "D". Or the prerequisite to satisfying "B" is some amount "D" that must be given to it and the prerequisite to satisfying "C" is some additional amount of "D" that must be given to it and we don't have enough of "D". A diagrammatic representation of this will look like:
