Cohesion and Coupling as Forces
We can use the gravity force as an analogy for cohesion and coupling. Cohesion would be planet Earth's gravity, pulling everything inward. Coupling would be the Sun, pulling planet Earth and keeping it in its orbit.
Using this analogy, too much cohesion would create a black hole, and too little cohesion would create a barren planet, unable to support life as we know it. The same applies for coupling. Too much coupling and planets would collide with each other or would be swallowed by the Sun; too little coupling and we would not have the Solar System because each planet would wander by itself in the Universe.
Coupling and cohesion are in reality the same force. Cohesion is felt inwards and coupling outwards. We believe this to be the fundamental force in object-oriented design, just as gravity is the essential force in Newton's laws. The secret to great design is finding a good balance between cohesion and coupling.
