This is a straight forward article!
If you run inventory systems (Make to Stock, MTS) and you have a constraint within the processes, it is highly unlikely that the system will be stable.
You will always be stocking out of something, somewhere!
If customer demand patterns change, it is really difficult to get stock into the system.
If you face a lot of stock outs, it is difficult to get those items into stock and NOT have other items go out of stock.
The inevitability is that the MTS system will slowly revert to an MTO (make to order) system as new orders come in and stock is not available.
Management of the inventory is an impossible task.
If you want an inventory system, you MUST have excess capacity available to service that inventory system.