Planning involves forecasts of various factors affecting activities. While forecasting conditions of raw-materials, competition, fashion, market trends, government policy, electricity, fuel, transportation etc. are considered. Thereafter, estimates about them are made. These estimates can never be 100% (cent percent) true because no factor is stable and any change in one factor affects other factors also. If planning is not changed in accordance with the change in the circumstances, it fails. Hence, it is said that flexibility is pre-condition of successful planning.