Have you ever thought about why we plan?  We plan to be more responsive to our needs. Examples are planning to travel or have dinner or send a shipment. If we did not plan we may not get what we want when we want it. Your favorite restaurant may not have enough space anymore or too late to make the shipment without advance notice to the trucking company.  Another important question is when do we plan or how far in advance do we need to plan? Too early, then there is a greater probability of things changing and rendering the plan useless. If you plan last minute then you risk not getting the desired outcome. We believe in the principle of least commitment planning. In other words do no plan until it is needed. Many factors decide on the timing. For example lead-times to get the right material into production and product in the market place dictate the timing of the planning. As General Eisenhower said, planning is important but re-planning is even more important. The latter implies that plans can change and need to be dynamic. Furthermore we need to re-plan fast in order to be more responsive. The faster we can respond, the less planning is needed. In the old days we used to have a detailed plan to meet someone at a certain location. Nowadays, thanks to our cell phones we hardly plan the details of our rendezvous. In other words we do not plan the details unless we need to. So how do we respond to surprise orders that come in? If your execution is fast enough then no problem. But very often this is not the case because of lead-time needed to get the material and building it unless you have inventory sitting around which can be very costly!  So to get around this you perform stochastic analysis and demand planning in order to decide what to build, what mix of products and at what levels of inventory you should keep in order to be most responsive, e.g. 98% delivery performance for certain SKU's and certain customers. The system would then show you the cost and risk related to such plans. In other words the cost of being so responsive or the reward of taking in additional market share from your competitors. Remember we plan for responsiveness and execute for reliability.  We also refer to this as planning for the unexpected or risk analysis. Have you planned for dinner yet or is it too early?