Kurt Lewin

In any situation there are both driving and restraining forces that influence any change that may occur.
Driving forces are those forces affecting a situation that are pushing in a particular direction; they tend to initiate a change and keep it going. In terms of improving productivity in a work group, pressure from a supervisor, incentive earnings, and competition may be examples of driving forces.
Restraining forces are forces acting to restrain or decrease the driving forces. Apathy, hostility, and poor maintenance of equipment may be examples of restraining forces against increased production. Equilibrium is reached when the sum of the driving forces equals the sum of the restraining forces.
This equilibrium, or present level of productivity, can be raised or lowered by changes in the relationship between the driving and the restraining forces.